builder: fix assembly-tests 3 of 4 failing (fixes #11433)

Author: medvednikov

vlib/v/builder/builder_test.v

@@ -265,3 +265,15 @@ fn test_macos_2048_build_does_not_force_deployment_target() {
 	assert flags_output.contains('-fobjc-arc')
 	assert !flags_output.contains('-mmacosx-version-min=')
 }
+
+fn test_macos_arch_flag_is_forwarded_to_c_compiler() {
+	$if !macos {
+		return
+	}
+	src_file := os.join_path(test_path, 'macos_arch_forwarding.v')
+	out_file := os.join_path(test_path, 'macos_arch_forwarding')
+	os.write_file(src_file, 'fn main() {\n\tprintln("hello")\n}\n')!
+	flags_output :=
+		run_v_ok('${os.quoted_path(vexe)} -gc none -showcc -skip-running -arch amd64 -o ${os.quoted_path(out_file)} ${os.quoted_path(src_file)}')
+	assert flags_output.contains('-arch x86_64')
+}

vlib/v/builder/cc.v

@@ -525,6 +525,17 @@ fn resolve_ccompiler_type(ccompiler string, fallback pref.CompilerType) pref.Com
 	return fallback
 }
 
+fn darwin_target_arch_name(arch pref.Arch) string {
+	return match arch {
+		.amd64 { 'x86_64' }
+		.arm64 { 'arm64' }
+		.i386 { 'i386' }
+		.ppc { 'ppc' }
+		.ppc64 { 'ppc64' }
+		else { '' }
+	}
+}
+
 fn cc_from_pref_ccompiler_type(cc_type pref.CompilerType) CC {
 	return match cc_type {
 		.tinyc { .tcc }
@@ -596,6 +607,12 @@ fn (mut v Builder) setup_ccompiler_options(ccompiler string) {
 	if ccoptions.cc == .unknown {
 		eprintln('Compilation with unknown C compiler `${cc_file_name}`')
 	}
+	if v.pref.os == .macos {
+		darwin_target_arch := darwin_target_arch_name(v.pref.arch)
+		if darwin_target_arch != '' {
+			ccoptions.args << ['-arch', darwin_target_arch]
+		}
+	}
 
 	// Add -fwrapv to handle UB overflows
 	if ccoptions.cc in [.gcc, .clang, .tcc]