cmd/dist, cmd/go: pass -arch for C compilation on Darwin

On Apple Silicon Mac, the C compiler has an annoying default
target selection, depending on the ancestor processes'
architecture. In particular, if the shell or IDE is x86, when
running "go build" even with a native ARM64 Go toolchain, the C
compiler defaults to x86, causing build failures. We pass "-arch"
flag explicitly to avoid this situation.

Fixes #43692.
Fixes #43476.
Updates golang/vscode-go#1087.

Change-Id: I80b6a116a114e11e273c6886e377a1cc969fa3f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/283812
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/cgo/gcc.go

@@ -1549,7 +1549,14 @@ func (p *Package) gccBaseCmd() []string {
 func (p *Package) gccMachine() []string {
  switch goarch {
  case "amd64":
+ if goos == "darwin" {
+ return []string{"-arch", "x86_64", "-m64"}
+ }
  return []string{"-m64"}
+ case "arm64":
+ if goos == "darwin" {
+ return []string{"-arch", "arm64"}
+ }
  case "386":
  return []string{"-m32"}
  case "arm":

src/cmd/go/internal/work/exec.go

@@ -2435,7 +2435,7 @@ func (b *Builder) fcExe() []string {
 func (b *Builder) compilerExe(envValue string, def string) []string {
  compiler := strings.Fields(envValue)
  if len(compiler) == 0 {
- compiler = []string{def}
+ compiler = strings.Fields(def)
  }
  return compiler
 }
@@ -2581,7 +2581,14 @@ func (b *Builder) gccArchArgs() []string {
  case "386":
  return []string{"-m32"}
  case "amd64":
+ if cfg.Goos == "darwin" {
+ return []string{"-arch", "x86_64", "-m64"}
+ }
  return []string{"-m64"}
+ case "arm64":
+ if cfg.Goos == "darwin" {
+ return []string{"-arch", "arm64"}
+ }
  case "arm":
  return []string{"-marm"} // not thumb
  case "s390x":

src/cmd/go/testdata/script/build_darwin_cc_arch.txt

@@ -0,0 +1,24 @@
+# Test that we pass -arch flag to C compiler on Darwin (issue 43692).
+
+[!darwin] skip
+[!cgo] skip
+
+# clear CC, in case user sets it
+env CC=
+
+env CGO_ENABLED=1
+
+env GOARCH=amd64
+go build -n -x c.go
+stderr 'clang.*-arch x86_64'
+
+env GOARCH=arm64
+go build -n -x c.go
+stderr 'clang.*-arch arm64'
+
+-- c.go --
+package main
+
+import "C"
+
+func main() {}

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

@@ -1749,12 +1749,19 @@ func hostlinkArchArgs(arch *sys.Arch) []string {
  switch arch.Family {
  case sys.I386:
  return []string{"-m32"}
- case sys.AMD64, sys.S390X:
+ case sys.AMD64:
+ if objabi.GOOS == "darwin" {
+ return []string{"-arch", "x86_64", "-m64"}
+ }
+ return []string{"-m64"}
+ case sys.S390X:
  return []string{"-m64"}
  case sys.ARM:
  return []string{"-marm"}
  case sys.ARM64:
- // nothing needed
+ if objabi.GOOS == "darwin" {
+ return []string{"-arch", "arm64"}
+ }
  case sys.MIPS64:
  return []string{"-mabi=64"}
  case sys.MIPS: