[dev.regabi] cmd/go: workaround -race issue on ppc64le

The race detector on ppc64le corrupts command-line arguments lists if
they contain an empty string, and cmd/go often generates compiler
argument lists containing `-D ""`. Since this is equivalent to not
specifying the `-D` flag at all, just do that. This allows using a
race-detector-enabled cmd/compile on ppc64le.

Updates #43883.

Change-Id: Ifac5cd9a44932129438b9b0b3ecc6101ad3716b2
Reviewed-on: https://go-review.googlesource.com/c/go/+/286173
Trust: Matthew Dempsky <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: mdempsky

src/cmd/go/internal/work/gc.go

@@ -129,7 +129,11 @@ func (gcToolchain) gc(b *Builder, a *Action, archive string, importcfg, embedcfg
 		}
 	}
 
-	args := []interface{}{cfg.BuildToolexec, base.Tool("compile"), "-o", ofile, "-trimpath", a.trimpath(), gcflags, gcargs, "-D", p.Internal.LocalPrefix}
+	args := []interface{}{cfg.BuildToolexec, base.Tool("compile"), "-o", ofile, "-trimpath", a.trimpath(), gcflags, gcargs}
+	if p.Internal.LocalPrefix != "" {
+		// Workaround #43883.
+		args = append(args, "-D", p.Internal.LocalPrefix)
+	}
 	if importcfg != nil {
 		if err := b.writeFile(objdir+"importcfg", importcfg); err != nil {
 			return "", nil, err