crt: Provide __p__osplatform() for all CRT import libraries

_osplatform is available only in i386 and x64 versions of msvcrt.dll,
msvcr70.dll, msvcr71.dll and msvcr80.dll.

Include emulation of __p__osplatform() functions for all other CRT
libraries, including UCRT.

Signed-off-by: Martin Storsjö <martin@martin.st>