backport fixes for libgomp
LoadLibrary/GetProcAddress on normaliz.dll doesn't work properly for w32 target
Wrong prototype, stdcall missing.
mingw64 (Win32 or Win64) with a w32 target does not link to normaliz.dll
Use -D_WIN32-WINNT=0x0600 -DWINVER=0x0600.
You don't really need a separate msys install, just use whatever that is working....
Fix math.h math constant visibility when using ...
merge from trunk up to r6471