cmd/go: silence ar with D flag failures

The first call of ar must not show its output in order to avoid useless
    error messages about D flag.
    The corresponding Go toolchain patch is CL 182077.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/183817

From-SVN: r272661

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-a857aad2f3994e6fa42a6fc65330e65d209597a0
+1d6578a20a9a2ee599a07f03cf7f8e7797d72b9c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/cmd/go/internal/work/gccgo.go

@@ -209,9 +209,16 @@ func (tools gccgoToolchain) pack(b *Builder, a *Action, afile string, ofiles []s
 	}
 	absAfile := mkAbs(objdir, afile)
 	// Try with D modifier first, then without if that fails.
-	if b.run(a, p.Dir, p.ImportPath, nil, tools.ar(), arArgs, "rcD", absAfile, absOfiles) != nil {
+	output, err := b.runOut(p.Dir, nil, tools.ar(), arArgs, "rcD", absAfile, absOfiles)
+	if err != nil {
 		return b.run(a, p.Dir, p.ImportPath, nil, tools.ar(), arArgs, "rc", absAfile, absOfiles)
 	}
+
+	if len(output) > 0 {
+		// Show the output if there is any even without errors.
+		b.showOutput(a, p.Dir, p.ImportPath, b.processOutput(output))
+	}
+
 	return nil
 }