This flag allows users on UNIX systems to set the tty for the program
being debugged by Delve. This is useful for debugging command line
applications which need access to their own TTY, and also for
controlling the output of the debugged programs so that IDEs may open a
dedicated terminal to show the output for the process.

* dwarf/line: implement DW_LNE_set_discriminator

We don't use the discriminator field in any way but we need to at least
parse it to support debub_line programs that use it.

* dwarf/line: support parsing DWARF4 debug_line sections

There is an extra field maximum_operations_per_instruction that is used
for VLIW CPUs. We don't support this feature but we have to at least
parse the field to not crash.

* gdbserial/gdbserver: Dynamically resolve debugserver binary

Instead of hardcoding the absolute path to the Command Line
Tools (CLT) binary, will attempt to resolve the path at the
$PATH, or at the Xcode bundle. If none are available, will
fallback to the default CLT location.

Fixes #986

* gdbserial/gdbserver: Log outgoing executed commands

Add logging to capture the executable and associated arguments used
in LLDBLaunch and LLDBAttach

Related to #986

* gdbserial/gdbserver: Add unit tests for helper function

Define unit tests for helper function. Setup each test to temporarily make
PATH variable, and file system changes, and subsequently revert them.

Related to #986

* gdbserial/gdbserver: Lazily load function

Lazily obtain absolute path to avoid increasing load times.

Remove flaky tests.

Related to #986

Adds a library of utility functions to generated breakpoint conditions
for next, step and stepout.

Fixes #1310

The test was always flaky because we can't fully control the state of
all goroutines in the target program, Go 1.14's asynchronous preemption
exacerbates the problem.

See for example:
https://travis-ci.com/github/go-delve/delve/jobs/302407282

This commit relaxes the checks made by the test to avoid irrelevante
flakiness.

Avoids constructing:

1. name of runtime.curg fields while executing parseG
2. the location expression while evaluating any variable.

Benchmark before:

BenchmarkConditionalBreakpoints-4   	       1	4953889884 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	4419775128 ns/op

Updates #1549

Under some circumstances (methods with non-pointer receivers or from
embedded fields called through an interface) the compiler will
autogenerate wrapper functions.

This commit changes next, step and stepout to skip all autogenerated
wrappers.

Fixes #1908

Replace the interface type Arch with a struct with the same
functionality.

Instead of selectively excluding this directory, hide it from the go
tooling by applying the "_" prefix.

Also cleanup some typos.

Allows Delve clients to stop a recording midway by sending a
Command('halt')
request.

This is implemented by changing debugger.New to start recording the
process on a separate goroutine while holding the processMutex locked.
By locking the processMutex we ensure that almost all RPC requests will
block until the recording is done, since we can not respond correctly
to any of them.
API calls that do not require manipulating or examining the target
process, such as "IsMulticlient", "SetApiVersion" and
"GetState(nowait=true)" will work while we are recording the process.

Two other internal changes are made to the API: both GetState and
Restart become asynchronous requests, like Command. Restart because
this way it can be interrupted by a StopRecording request if the
rerecord option is passed.
GetState because clients need a call that will block until the
recording is compelted and can also be interrupted with a
StopRecording.

Clients that are uninterested in allowing the user to stop a recording
can ignore this change, since eventually they will make a request to
Delve that will block until the recording is completed.

Clients that wish to support this feature must:

1. call GetState(nowait=false) after connecting to Delve, before any
   call that would need to manipulate the target process
2. allow the user to send a StopRecording request during the initial
   GetState call
3. allow the user to send a StopRecording request during any subsequent
   Restart(rerecord=true) request (if supported).

Implements #1747

Reset the timer once we start executing the code paths we actually care
to measure, since the setup and continue steps can be relatively
expensive.

Also, disable recording on benchmarks. This seems less useful, and also
cuts out a lot of noise when benchmarks are run.

This patch moves out unrelated types, variables and functions from
proc.go into a place where they make more sense.

When switching to the goroutine stack the stack iterator registers
might not have any entry for the BP register, make sure to add it
instead of just trying to change it.

Instead of rescanning debug_info every time we want to read a function
(either to find inlined calls or its variables) cache the tree of
dwarf.Entry that we would generate and use that.

Benchmark before:

BenchmarkConditionalBreakpoints-4   	       1	5164689165 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	4817425836 ns/op

Updates #1549

Add logging for Issue #1927. The bug happens during the call to
api.ConvertThread, returning an error will not suffice since
ConvertThread will not surface it.

Updates #1927

Inserts a call to ClearAllGCache into stepInstructionOut so that cached
goroutine state is not inconsistent after an injected function call.\

Fixes #1925

Implements #1256

Autogenerates .travis.yml configuration using the contents of
pkg/goversion/compat.go.
Also:
- excludes testing of windows/amd64/tip and linux/arm64/tip (Travis-CI
  can't get Go at tip for those combinations).
- Removes Go 1.11 from pkg/goversion/compat.go which we don't test
  anymore.

If we call one expression which is the fake method of meanless
string, `delve` will panic. Strengthen the inspection of boundary
conditions when supporting function calls on non-struct types.

Update: #1871

* *: Fix go vet struct complaints

* *: Fix struct vet issue on linux

* *: Ignore proc/native in go vet check

We have to do some unsafe pointer manipulation that will never make go
vet happy within the proc/native package. Ignore it for runs of go vet.

* proc: move defer breakpoint code into a function

Moves the code that sets a breakpoint on the first deferred function,
used by both next and StepOut, to its function.

* proc: implement reverse step/next/stepout

When the direction of execution is reversed (on a recording) Step, Next and
StepOut will behave similarly to their forward version. However there are
some subtle interactions between their behavior, prologue skipping, deferred
calls and normal calls. Specifically:

- when stepping backwards we need to set a breakpoint on the first
  instruction after each CALL instruction, once this breakpoint is reached we
  need to execute a single StepInstruction operation to reverse step into the
  CALL.
- to insure that the prologue is skipped reverse next needs to check if it
  is on the first instruction after the prologue, and if it is behave like
  reverse stepout.
- there is no reason to set breakpoints on deferred calls when reverse
  nexting or reverse stepping out, they will never be hit.
- reverse step out should generally place its breakpoint on the CALL
  instruction that created the current stack frame (which will be the CALL
  instruction immediately preceding the instruction at the return address).
- reverse step out needs to treat panic calls and deferreturn calls
  specially.

* service,terminal: implement reverse step, next, stepout

Update: #1879

Benchmark before:

BenchmarkConditionalBreakpoints-4   	       1	7031242832 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	5282482841 ns/op

Conditional breakpoint evaluation latency: 0.70ms -> 0.52ms

Updates #1549

* proc,proc/*: move SelectedGoroutine to proc.Target, remove PostInitializationSetup

moves SelectedGoroutine, SwitchThread and SwitchGoroutine to
proc.Target, merges PostInitializationSetup with NewTarget.

* proc,proc/*: add StopReason field to Target

Adds a StopReason field to the Target object describing why the target
process is currently stopped. This will be useful for the DAP server
(which needs to report this reason in one of its requests) as well as
making pull request #1785 (reverse step) conformant to the new
architecture.

* proc: collect NewTarget arguments into a struct

Implement debugging function for 386 on linux with reference to AMD64.
There are a few remaining problems that need to be solved in another time.

1. The stacktrace of cgo are not exactly as expected.
2. Not implement `core` for now.
3. Not implement `call` for now. Can't not find `runtime·debugCallV1` or
   similar function in $GOROOT/src/runtime/asm_386.s.

Update #20

* proc/native/linux: only set breakpoints on threads that receive SIGTRAP

* proc/native/linux: do not call (*Thread).Stopped inside (*Process).stop

(*Thread).Stopped is slow because it needs to open, read and parse a
file in /proc, we don't actually need to do that, we can just rely on
the value of Thread.os.running.

Benchmark before:

BenchmarkConditionalBreakpoints-4              1        12476166303 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	10403533675 ns/op

Conditional breakpoint evaluation: 1.24ms -> 1ms

Updates #1549

* logflags: Add pid to server-listening-at message

* Address review comments: use logger
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

There are too many commands, for clarity they should be divided into
categories when printing and generating documentation.