message: Add comment about why Windows is using clang++
diff: @@ -187,6 +187,8 @@ fn run_c_compile(
  ) -> anyhow::Result<()> {
  #[cfg(not(windows))]
  let c_compiler = "cc";
  + // We must use a C++ compiler on Windows because wasm.h uses `static_assert`
  + // which isn't available in `clang` on Windows.
  #[cfg(windows)]
  let c_compiler = "clang++";
  