Update to support MSYS2/GCC

[jalius]

Adding build support for MSYS2/GCC and cleaning up some various build errors.

• Fix implementation of osal_thread_create() to match declaration.
• Fix missing timezone struct declaration.
• Add GCC style struct packing
• Update CMakeLists with non-MSVC win32 build instructions
• Address some compiler warnings arising from unused parameters and variables.
• Remove stdint.h and inttypes.h which are MSVC specific. The compiler should find these standard library files based on the target rather than including them in the project.

It now builds properly on MSYS2/GCC using cmake generators "MSYS Makefiles" and "Ninja".

I didn't get a chance to build it again with MSVC, so should probably do that before merging.

[jalius]

Wondering if we should change
int osal_thread_create(void *thandle, int stacksize, void *func, void *param)
parameter void *thandle to OSAL_THREAD_HANDLE *thandle
for clarity in all implementations.