debug: gcflags set by user should be ignored when debugging

[ramya-rao-a]

As described in microsoft/vscode-go#2415, gcflags set by the user interferes with debugging. This issue is to have the extension ignore this setting when debugging.

While microsoft/vscode-go#2415 is about debugging tests, this may apply to normal debugging as well

[stamblerre]

@hyangah: How do you feel about this? I am nervous the ignore any user-set flags, and would maybe prefer to surface an error message.

[ramya-rao-a]

This would be similar to the other issue where we have user set GOOS and GOARCH. Basically user settings that would mess with delve

[hyangah]

Removing gcflags, GOOS, GOARCH when launching through debugger makes sense. We will do it.
To avoid user confusion, we need to notify users of this modification when those conflicting settings are detected.

/cc @suzmue @polinasok

@suzmue also questioned whether we should apply similar changes on GOOS/GOARCH when running tests.

[gopherbot]

Change https://golang.org/cl/265580 mentions this issue: src/goDebugConfiguration: remove user set '--gcflags' from config

[szmcdull]

Hi, I need -gcflags='-G=3' to enable generics. But seems vscode cannot do this. Neither gopls nor dlv-dap is using the gcflags and they all complain about grammar error which is valid when generics is enabled

[polinasok]

@szmcdull If you want dlv to build things for you, then it will supply its own gcflags. If you prefer to customize those, then you can build the binary directly and let dlv/vscode execute it with exec mode.