cmd/gomobile: iphonesimulator target

This enables building for iphonesimulator-arm64 and merging into a fat
XCFramework that also may include ios/arm64.

This should fix golang/go#47212 (comment)

Note: tests are broken. Will fix in a followup commit.

cmd/gomobile/build.go

@@ -363,6 +363,12 @@ func parseBuildTarget(buildTarget string) (targetPlatforms, targetArchs []string
 		return nil, nil, fmt.Errorf(`invalid target ""`)
 	}
 
+	// TODO(ydnar): preserve existing behavior where -target=ios
+	// builds for iphonesimulator as well.
+	if buildTarget == "ios" {
+		buildTarget = "ios,iphonesimulator"
+	}
+
 	platforms := map[string]bool{}
 	archs := map[string]bool{}
 

cmd/gomobile/env.go

@@ -33,11 +33,13 @@ func isDarwinPlatform(platform string) bool {
 	return contains(darwinPlatforms, platform)
 }
 
-var darwinPlatforms = []string{"ios", "maccatalyst", "macos"}
+var darwinPlatforms = []string{"ios", "iphonesimulator", "maccatalyst", "macos"}
 
 func platformArchs(platform string) []string {
 	switch platform {
 	case "ios":
+		return []string{"arm64"}
+	case "iphonesimulator":
 		return []string{"arm64", "amd64"}
 	case "macos", "maccatalyst":
 		return []string{"arm64", "amd64"}
@@ -57,7 +59,7 @@ func platformOS(platform string) string {
 	switch platform {
 	case "android":
 		return "android"
-	case "ios":
+	case "ios", "iphonesimulator":
 		return "ios"
 	case "macos", "maccatalyst":
 		return "darwin"
@@ -70,7 +72,7 @@ func platformTags(platform string) []string {
 	switch platform {
 	case "android":
 		return []string{"android"}
-	case "ios":
+	case "ios", "iphonesimulator":
 		return []string{"ios"}
 	case "macos":
 		return []string{"macos"}
@@ -205,16 +207,14 @@ func envInit() (err error) {
 			switch platform {
 			case "ios":
 				goos = "ios"
-				switch arch {
-				case "arm64":
-					sdk = "iphoneos"
-					clang, cflags, err = envClang(sdk)
-					cflags += " -miphoneos-version-min=" + buildIOSVersion
-				case "amd64":
-					sdk = "iphonesimulator"
-					clang, cflags, err = envClang(sdk)
-					cflags += " -mios-simulator-version-min=" + buildIOSVersion
-				}
+				sdk = "iphoneos"
+				clang, cflags, err = envClang(sdk)
+				cflags += " -miphoneos-version-min=" + buildIOSVersion
+			case "iphonesimulator":
+				goos = "ios"
+				sdk = "iphonesimulator"
+				clang, cflags, err = envClang(sdk)
+				cflags += " -mios-simulator-version-min=" + buildIOSVersion
 			case "maccatalyst":
 				goos = "darwin"
 				sdk = "macosx"