cmd/internal/ld, cmd/dist: support -buildmode=c-archive on linux

Change-Id: I8c97751a79b57197428b0f0b66fc9575708a2eb0
Reviewed-on: https://go-review.googlesource.com/8979
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/dist/test.go

@@ -272,8 +272,7 @@ func (t *tester) registerTests() {
 		} else if t.hasBash() && t.goos != "android" && !iOS {
 			t.registerTest("testso", "../misc/cgo/testso", "./test.bash")
 		}
-		if t.extLink() && t.goos == "darwin" && t.goarch == "amd64" {
+		if t.buildmode("c-archive") {
-			// TODO(crawshaw): add darwin/arm{,64}
 			t.registerTest("testcarchive", "../misc/cgo/testcarchive", "./test.bash")
 		}
 		if t.gohostos == "linux" && t.goarch == "amd64" {
@@ -370,6 +369,26 @@ func (t *tester) extLink() bool {
 	return false
 }
 
+func (t *tester) buildmode(mode string) bool {
+	switch mode {
+	case "c-archive":
+		switch {
+		case !t.extLink():
+			return false
+		case t.goos == "darwin" && t.goarch == "amd64":
+			// TODO(crawshaw): add darwin/arm{,64}
+			return true
+		case t.goos == "linux" && t.goarch == "amd64":
+			return true
+		default:
+			return false
+		}
+	default:
+		log.Fatal("internal error: unknown buildmode %s", mode)
+		return false
+	}
+}
+
 func (t *tester) cgoTest() error {
 	env := mergeEnvLists([]string{"GOTRACEBACK=2"}, os.Environ())
 

src/cmd/internal/ld/lib.go

@@ -288,7 +288,9 @@ func (mode *BuildMode) Set(s string) error {
 	case "exe":
 		*mode = BuildmodeExe
 	case "c-archive":
-		if goos != "darwin" {
+		switch goos {
+		case "darwin", "linux":
+		default:
 			return badmode()
 		}
 		*mode = BuildmodeCArchive