cmd/go: quote parentheses when outputting command

A gccgo command line can contain parentheses, for -( and -).
Quote them when outputting a command line, so that `go build -x`
output is suitable for use as shell input.

Change-Id: I43194b87bf048e583c222b19ca4bcdcb1deca97a
Reviewed-on: https://go-review.googlesource.com/111635
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/work/exec.go

@@ -1580,7 +1580,9 @@ func joinUnambiguously(a []string) string {
 			buf.WriteByte(' ')
 		}
 		q := strconv.Quote(s)
-		if s == "" || strings.Contains(s, " ") || len(q) > len(s)+2 {
+		// A gccgo command line can contain -( and -).
+		// Make sure we quote them since they are special to the shell.
+		if s == "" || strings.ContainsAny(s, " ()") || len(q) > len(s)+2 {
 			buf.WriteString(q)
 		} else {
 			buf.WriteString(s)