cmd/link: on Mach-O, generate LC_UUID by default

On Mach-O, default to "-B gobuildid", so it generates the UUID
based on Go buildid by default.

Fixes #68678.

Cq-Include-Trybots: luci.golang.try:gotip-darwin-amd64_14,gotip-darwin-arm64_13
Change-Id: I6c1a6bcafd8370a13174657e05d7d9620a8d4f12
Reviewed-on: https://go-review.googlesource.com/c/go/+/618598
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: cherrymui

src/cmd/link/internal/ld/elf.go

@@ -807,6 +807,9 @@ func elfwritefreebsdsig(out *OutBuf) int {
 
 func addbuildinfo(ctxt *Link) {
 	val := *flagHostBuildid
+	if val == "" || val == "none" {
+		return
+	}
 	if val == "gobuildid" {
 		buildID := *flagBuildid
 		if buildID == "" {

src/cmd/link/internal/ld/main.go

@@ -95,7 +95,7 @@ var (
 	flagN             = flag.Bool("n", false, "no-op (deprecated)")
 	FlagS             = flag.Bool("s", false, "disable symbol table")
 	flag8             bool // use 64-bit addresses in symbol table
-	flagHostBuildid   = flag.String("B", "", "set ELF NT_GNU_BUILD_ID `note` or Mach-O UUID; use \"gobuildid\" to generate it from the Go build ID")
+	flagHostBuildid   = flag.String("B", "", "set ELF NT_GNU_BUILD_ID `note` or Mach-O UUID; use \"gobuildid\" to generate it from the Go build ID; \"none\" to disable")
 	flagInterpreter   = flag.String("I", "", "use `linker` as ELF dynamic linker")
 	flagCheckLinkname = flag.Bool("checklinkname", true, "check linkname symbol references")
 	FlagDebugTramp    = flag.Int("debugtramp", 0, "debug trampolines")
@@ -294,9 +294,10 @@ func Main(arch *sys.Arch, theArch Arch) {
 		*flagBuildid = "go-openbsd"
 	}
 
-	if *flagHostBuildid != "" {
-		addbuildinfo(ctxt)
+	if *flagHostBuildid == "" && *flagBuildid != "" && ctxt.IsDarwin() {
+		*flagHostBuildid = "gobuildid"
 	}
+	addbuildinfo(ctxt)
 
 	// enable benchmarking
 	var bench *benchmark.Metrics