[windows] Implement GetProcAddress internally to avoid initializing the CRT

ASan uses GetProcAddress to get the address of malloc so it can patch
it. Newer versions of Windows make GetProcAddress initialize the DLL
before returning a function pointer into it. That's perfectly
reasonable, but ASan needs to finish patching malloc before CRT
initialization. So now we roll our own GetProcAddress.

Fixes PR24237

Based on a patch by David Major

Originally written by David Major as part of:
https://hg.mozilla.org/mozilla-central/file/tip/toolkit/xre/WindowsCrtPatch.h

llvm-svn: 245377