windows: add ARM64 support

This was actually surprising once I got TinyGo to build on Windows 11
ARM64. All the changes are exactly what you'd expect for a new
architecture, there was no special weirdness just for arm64.

Actually getting TinyGo to build was kind of involved though. The very
short summary is: install arm64 versions of some pieces of software
(like golang, cmake) instead of installing them though choco. In
particular, use the llvm-mingw[1] toolchain instead of using standard
mingw.

[1]: https://github.com/mstorsjo/llvm-mingw/releases

builder/builder_test.go

@@ -59,6 +59,7 @@ func TestClangAttributes(t *testing.T) {
 		{GOOS: "darwin", GOARCH: "amd64"},
 		{GOOS: "darwin", GOARCH: "arm64"},
 		{GOOS: "windows", GOARCH: "amd64"},
+		{GOOS: "windows", GOARCH: "arm64"},
 	} {
 		name := "GOOS=" + options.GOOS + ",GOARCH=" + options.GOARCH
 		if options.GOARCH == "arm" {