cmd/dist, make.bash: darwin/arm support

cmd/dist: recognize darwin/arm as (host) goos/goarches. also hard
          code GOARM=7 for darwin/arm.
make.bash: don't pass -mmacosx-version-min=10.6 when building for
           darwin/arm.

Change-Id: If0ecd84a5179cd9bb61b801ac1899adc45f12f75
Reviewed-on: https://go-review.googlesource.com/2126Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/dist/build.go

@@ -617,7 +617,7 @@ func install(dir string) {
 		}
 		// disable word wrapping in error messages
 		gccargs = append(gccargs, "-fmessage-length=0")
-		if gohostos == "darwin" {
+		if gohostos == "darwin" && gohostarch != "arm" {
 			// golang.org/issue/5261
 			gccargs = append(gccargs, "-mmacosx-version-min=10.6")
 		}

src/cmd/dist/util.go

@@ -376,7 +376,7 @@ func main() {
 
 	if gohostarch == "" {
 		// Default Unix system.
-		out := run("", CheckExit, "uname", "-m")
+		out := run("", CheckExit, "uname", "-m", "-v")
 		switch {
 		case strings.Contains(out, "x86_64"), strings.Contains(out, "amd64"):
 			gohostarch = "amd64"
@@ -388,6 +388,10 @@ func main() {
 			gohostarch = "ppc64le"
 		case strings.Contains(out, "ppc64"):
 			gohostarch = "ppc64"
+		case gohostos == "darwin":
+			if strings.Contains(out, "RELEASE_ARM_") {
+				gohostarch = "arm"
+			}
 		default:
 			fatal("unknown architecture: %s", out)
 		}
@@ -453,6 +457,12 @@ func xgetgoarm() string {
 		// NaCl guarantees VFPv3 and is always cross-compiled.
 		return "7"
 	}
+	if goos == "darwin" {
+		// Assume all darwin/arm devices are have VFPv3. This
+		// port is also mostly cross-compiled, so it makes little
+		// sense to auto-detect the setting.
+		return "7"
+	}
 	if gohostarch != "arm" || goos != gohostos {
 		// Conservative default for cross-compilation.
 		return "5"