cmd/cgo: add line info for return statements
cmd/cgo: add line info for return statements

When calling a C function, line information will be
incorrect if the function call's closing parenthesis
is not on the same line as the last argument. We add
a comment with the line info for the return statement
to guide debuggers to the correct line.

Fixes #49839.

Change-Id: I8bc2ce35fec9cbcafbbe8536d5a79dc487eb24bb
GitHub-Last-Rev: 8b28646d2e25b19272ded7a3d54b9374108a54e2
GitHub-Pull-Request: golang/go#49840
Reviewed-on: https://go-review.googlesource.com/c/go/+/367454
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>

nawawi/go,nawawi/go,golang/go,golang/go,nawawi/go,golang/go,golang/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go