Undefine 'near' and 'far' in mat4.h for host Windows

Previously, when a C++ file included 'windows.h' and subsequently
included 'mat4.h', a compile error occurred. This is because, for some
esoteric/obsolete reasons, 'windows.h' includes empty definitions of
'near' and 'far'. These conflict with the usage of 'near' and 'far' in
'mat4.h'.

Add some logic to 'mat4.h' for host Windows that undefines 'near' and
'far' to avoid these conflicts.

Test: Build libandroid_runtime on Windows
Bug: 328307399
Change-Id: I13d068e7f800cf370a0f7d9f1b98479f9c6aeb35