all: add macOS support

target.go

@@ -189,6 +189,9 @@ func LoadTarget(target string) (*TargetSpec, error) {
 			return nil, errors.New("expected a full LLVM target or a custom target in -target flag")
 		}
 		goos := tripleSplit[2]
+		if strings.HasPrefix(goos, "darwin") {
+			goos = "darwin"
+		}
 		goarch := map[string]string{ // map from LLVM arch to Go arch
 			"i386":    "386",
 			"x86_64":  "amd64",
@@ -211,11 +214,15 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 		BuildTags: []string{goos, goarch},
 		Compiler:  commands["clang"],
 		Linker:    "cc",
-		LDFlags:   []string{"-no-pie", "-Wl,--gc-sections"}, // WARNING: clang < 5.0 requires -nopie
 		Objcopy:   "objcopy",
 		GDB:       "gdb",
 		GDBCmds:   []string{"run"},
 	}
+	if goos == "darwin" {
+		spec.LDFlags = append(spec.LDFlags, "-Wl,-dead_strip")
+	} else {
+		spec.LDFlags = append(spec.LDFlags, "-no-pie", "-Wl,--gc-sections") // WARNING: clang < 5.0 requires -nopie
+	}
 	if goarch != runtime.GOARCH {
 		// Some educated guesses as to how to invoke helper programs.
 		if goarch == "arm" && goos == "linux" {