Implements #596

The compiler a variable 'v' that escapes to the heap with a '&v' entry.
Auto dereference those local variables.

Fixe #871

While we are waiting for the process to exit in native.(*Process).Kill
we could receive queued exception events, those must be continued or
the wait will never finish.

Fixes #940

Always pick a goroutine that we know will have to be resumed before the
program terminates instead of relying on luck.

Fixes #803

This is a "fix" for the issue of being unable to see the source when setting a breakpoint on main.init.

Fixes #922

Our tests are not designed to be run in parallel, for example there are
multiple tests in disparate packages all trying to run textnextnethttp
which will compete for access to port 9191, we shouldn't let tests run
in parallel.

By specifying the -a flag we insure that all packages are recompiled
with -gcflags='-N -l'. Previously -a could not be specified because the
compiler could not compile runtime without optimizations.

Fixes #738

Fixes #106

go1.9 no longer needs "linkmode internal" on windows.

Fixes #755
Fixes #477
Fixes #631

Before go1.9 embedded struct fields had name == "" in runtime and ==
type name in DWARF. After go1.9 both runtime and DWARF use a simplified
version of the type as name.
Embedded structs are distinguished from normal fields by setting a flag
in the runtime.structfield, for runtime, and by adding a custom
attribute in DWARF.

Splits out type parsing and go-specific Type hierarchy from
x/debug/dwarf, replace x/debug/dwarf with debug/dwarf everywhere,
remove x/debug/dwarf from vendoring.

The compiler a variable 'v' that escapes to the heap with a '&v' entry.
Auto dereference those local variables.

Fixe #871

Can't get the trace directory from the server after we disconnect from
it.

Instead of panicing for sending on a closed channel, detect that the
process has exited and return a proper error message.

This patch also cleans up some spots where the Pid is omitted from the
error.

Fixes #920

Mozilla RR will create a trace directory that can be reused with the
replay verb, however if we delete the executable file the trace
directory will become useless, so delete that too before exit.

Users that wish to reuse a recording should build the executable
themselves and then use either dlv exec or rr record to do the
recording.

If the user tries to list the contents of a function pointer but
forgets the '*' operator the location lookup will fail and result in a
unhelpful "location not found" error.

Instead if the location lookup fails we should try interpreting the
locspec as if it was preceded by '*'.

* proc/native: make sure debugged executable can be deleted on windows

Delve opens debugged executable to read binary info it
contains, but it never closes the file. Windows will not
let you delete file that is opened. So close Process.bi
in Process.postExit, and actually call Process.postExit
from windows Process.Kill.

Also Windows sends some debugging events
(EXIT_PROCESS_DEBUG_EVENT event in particular) after Delve
calls TerminateProcess. The events need to be consumed by
debugger before debugged process will be released by
Windows. So call Process.waitForDebugEvent after
TerminateProcess in Process.Kill.

Fixes #398

* cmd/dlv: make TestIssue398 pass on darwin

* cmd/dlv: add comment for TestIssue398

* proc/native: wait for debuggee to exit before returning from windows Process.Kill

* proc/native: close process handle before returning from windows killProcess

* proc/native: remove not used Process.Process

Updates #893

When stepping through runtime sometimes the current goroutine will
change. It is impossible to handle this in Next, Step and StepOut but
StepInstruction can reset the current goroutine correctly.

When the process exits during we used to return an error, but after
commit 8bbcc89711f4263e7bb2b6d9c00fa96d0294e56f we move the error into
state.Err. Revert this behavior change.

Updates #893

proc.Process.StepInstruction should work even if there is no goroutine
selected.

If one of the expressions that are automatically evaluated when a
breakpoint is hit can't be evaluated breakpoint information collection
should continue and the error should be returned for that specific
expression instead of the whole command.

Next will add internal breakpoints with nil condition if it can't find
the current goroutine (possibly because there isn't a current goroutine
because the runtime hasn't been initialized yet).
onNextGoroutine should skip breakpoints with nil condition, otherwise
we'll end up with an internal debugger error trying to walk a nil
expression.

Updates #893

When there's a error reading the stack trace the call stack itself
could be corrupted and we should return the partial stacktrace that we
have.

Fixes #868

Updates #794

When location spec is given and the base can be interpreted either in
source file name or function name, NomalLocationSpec searches both
the source file list and the function symbol list, and selects matching
candidates. Previously, all the matching candidates were added to one
single list regardless whether the candidate was from the source file
list or not. Then, later, Find tries to guess whether the candiate
was a function or a file based on a heuristic, i.e, whether the
candidate is an absolute file path. The heuristic is fragile - since
there is no guarantee that the included source file name is an absolute
path.

Instead, this CL preserves where the candidate was found; file list or
function symbol list. Then, use that info to determine whether the
candidate is a source file name or not.

Variable lookup is slow because it requires a full scan of debug_info
to check for package variables, this doesn't matter much in interactive
use but can slow down evaluation of breakpoint conditions
significantly.

Providing benchmark proof for this is hard since this effect doesn't
show for small programs with small debug_info sections.

* proc: fix interaction of RequestManualStop and conditional breakpoints

A conditional breakpoint that is hit but has the condition evaluate to
false can block a RequestManualStop from working. If the conditional
breakpoint is set on an instruction that is executed very frequently by
multiple goroutines (or many conditional breakpoints are set) it could
prevent all calls to RequestManualStop from working.

This commit fixes the problem by changing proc.Continue to exit
unconditionally after a RequestManualStop is called.

* proc/gdbserial: fix ContinueOnce getting stuck on macOS

Fixes #902

Fixes #904

The concrete value of an interface is always stored as a pointer inside
an interface variable. So far we have followed the memory layout and
reported the type of the 'data' attribute of interfaces as a pointer,
however this makes it impossible to distinguish interfaces with
concrete value of type 'A' from interfaces of concrete value of type
'*A'.

With this changeset when we autodereference pointers when the concrete
type of an interface is not a pointer.