crt: Provide __p__winver() function also for ARM msvcrt.dll import library

ARM32 and ARM64 OS system version of msvcrt.dll do not have neither _winver
global variable, nor __p__winver() function. But they have _winmajor and
_winminor global variables.

Provide __p__winver() function emulation for ARM msvcrt import library via
via values of _winmajor and _winminor global variables.

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