cmd/go: don't generate DWARF in the compiler if the linker will discard it

Change-Id: I7610f968f5c22b51a6a8813d6f31ccb772a12ba9
Reviewed-on: https://go-review.googlesource.com/40858
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/work/build.go

@@ -2203,6 +2203,9 @@ func (gcToolchain) gc(b *Builder, p *load.Package, archive, obj string, asmhdr b
 	if p.Internal.BuildID != "" {
 		gcargs = append(gcargs, "-buildid", p.Internal.BuildID)
 	}
+	if p.Internal.OmitDebug {
+		gcargs = append(gcargs, "-dwarf=false")
+	}
 
 	for _, path := range p.Imports {
 		if i := strings.LastIndex(path, "/vendor/"); i >= 0 {