On linux platform, we simply treated `/proc/$pid/exe` as the
executable of targeting process when doing `dlv attach`. The
`/proc/$pid/exe` is a symbol link of the real executable file.
Delve couldn't find the corrsponding external debug file based on the
symbol link:

```
could not attach to pid $pid: could not open debug info
```

The fix is to evaluate the symbol links to the actual executable path.

Allow user to specify output syntax flavor of assembly in the
disassemble command.

Close #415

This test will occasionally hang in SetBreakpoint/WriteMemory

The process could quit while we are inside stop, we should report the
error otherwise the following code will try to send on the closed
ptrace channel.
Fixes a sporadic error in TestIssue1101.

Reduces test timeout by one minute so that Go will timeout before
Travis-CI and report useful informations about the hang.

Fixes a long standing dangling TODO item.

Embed the debugger config object in the service config object to avoid needless duplication of fields.

We should not return error directly which set `fileFound` to be true
if there's a compileUnit without line section.

Commit changes after executing gen-usage-docs.go script

Related to #1995

Add --continue as a valid flag for the attach command by decorating attachCommand
with the continueOnStart variable.

Fixes #1995

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

1. Adds a note to the documentation describing how to use 'go get' in
   modules mode
2. Removes the '-u' option which, when 'go get' is used incorrectly
   will make 'go' try to compile Delve with unsupported dependencies
3. Removed obsolete note about Go 1.5 vendor experiment.

Fixes #1988

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

Fixes #1310

Clear all physical breakpoints associated with a logical breakpoint in
ClearBreakpoint.

Fixes #1955

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

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.

Remove gitignore rule preventing vendor/modules.txt file from being
commited, add check that the vendor directory is synchronized.

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.