mingw-w64-headers/crt/corecrt.h: fix cygwin w32api usage

Cygwin suppresses uintptr_t typedefs to avoid polluting its own
CRT headers. This breaks any use of the type, yet including stdint.h
further pollutes the namespace.

Use __UINTPTR_TYPE__ directly in _invalid_parameter and _invoke_watson
since it is supported by both gcc and clang.

Signed-off-by: Jonathan Yong <10walls@gmail.com>