[release-branch.go1.15] cmd/link: pass arch-specific flags to external linker when testing supported flag

When testing if a flag (e.g. "-no-pie") is supported by the
external linker, pass arch-specific flags (like "-marm").

In particular, on the ARM builder, if CGO_LDFLAGS=-march=armv6
is set, the C toolchain fails to build if -marm is not passed.

	# cc -march=armv6 1.c
	1.c: In function 'main':
	1.c:3:1: sorry, unimplemented: Thumb-1 hard-float VFP ABI
	 int main() {
	 ^~~

This makes the Go linker think "-no-pie" is not supported when it
actually is.

Passing -marm makes it work.

Fixes #46684.

Change-Id: I4e8b71f08818993cbbcb2494b310c68d812d6b50
Reviewed-on: https://go-review.googlesource.com/c/go/+/278592
Trust: Cherry Zhang <[email protected]>
Run-TryBot: Cherry Zhang <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
(cherry picked from commit a318d56)
Reviewed-on: https://go-review.googlesource.com/c/go/+/326711
Run-TryBot: Carlos Amedee <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Trust: Dmitri Shuralyov <[email protected]>

Author: cherrymui

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

@@ -1555,7 +1555,7 @@ func (ctxt *Link) hostlink() {
 	}
 
 	const compressDWARF = "-Wl,--compress-debug-sections=zlib-gnu"
-	if ctxt.compressDWARF && linkerFlagSupported(argv[0], altLinker, compressDWARF) {
+	if ctxt.compressDWARF && linkerFlagSupported(ctxt.Arch, argv[0], altLinker, compressDWARF) {
 		argv = append(argv, compressDWARF)
 	}
 
@@ -1645,7 +1645,7 @@ func (ctxt *Link) hostlink() {
 	if ctxt.BuildMode == BuildModeExe && !ctxt.linkShared {
 		// GCC uses -no-pie, clang uses -nopie.
 		for _, nopie := range []string{"-no-pie", "-nopie"} {
-			if linkerFlagSupported(argv[0], altLinker, nopie) {
+			if linkerFlagSupported(ctxt.Arch, argv[0], altLinker, nopie) {
 				argv = append(argv, nopie)
 				break
 			}
@@ -1746,7 +1746,7 @@ func (ctxt *Link) hostlink() {
 
 var createTrivialCOnce sync.Once
 
-func linkerFlagSupported(linker, altLinker, flag string) bool {
+func linkerFlagSupported(arch *sys.Arch, linker, altLinker, flag string) bool {
 	createTrivialCOnce.Do(func() {
 		src := filepath.Join(*flagTmpdir, "trivial.c")
 		if err := ioutil.WriteFile(src, []byte("int main() { return 0; }"), 0666); err != nil {
@@ -1780,7 +1780,7 @@ func linkerFlagSupported(linker, altLinker, flag string) bool {
 		"-target",
 	}
 
-	var flags []string
+	flags := hostlinkArchArgs(arch)
 	keep := false
 	skip := false
 	extldflags := strings.Fields(*flagExtldflags)