Platform: make `stdint` module implicit on Windows
This makes the `stdint` module implicit which repairs the ability to
build some components. In order to accomplish this, we need to
potentially break the fragile Swift build system. Due to the incorrect
handling of compilers we need some workarounds to support
cross-compilation. This removes the injected system header paths when
building on Windows to ensure that the clang resource headers are not
following the system headers which breaks the modules as the clang
resources are dependent on the system headers when running in hosted
mode.
