cleanup(platform): we don't need CGO anymore (#355)

* cleanup(platform): we don't need CGO anymore

Since go1.16, we have the `ios` port. So we can easily
disambiguate between ios and darwin.

This means we don't need to rely on CGO to correctly guess
whether we are on ios or darwin anymore.

So, now miniooni does not depend on a C compiler even
when you are not cross compiling.

* Update internal/platform/platform.go

internal/platform/platform.go

@@ -24,28 +24,20 @@ import "runtime"
 // has been disabled. In such case, the code will return "ios" when
 // using arm{,64} and "macos" when using x86{,_64}.
 func Name() string {
-	if name := cgoname(); name != "unknown" {
-		return name
-	}
-	return puregoname(runtime.GOOS, runtime.GOARCH)
+	return name(runtime.GOOS)
 }
 
-func puregoname(goos, goarch string) string {
+// name is a utility function for implementing Name.
+func name(goos string) string {
+	// Note: since go1.16 we have the ios port, so the ambiguity
+	// between ios and darwin is now gone.
+	//
+	// See https://golang.org/doc/go1.16#darwin
 	switch goos {
-	case "android", "linux", "windows":
+	case "android", "linux", "windows", "ios":
 		return goos
 	case "darwin":
-		return detectDarwin(goarch)
-	}
-	return "unknown"
-}
-
-func detectDarwin(goarch string) string {
-	switch goarch {
-	case "386", "amd64":
 		return "macos"
-	case "arm", "arm64":
-		return "ios"
 	}
 	return "unknown"
 }