contribs: glew: Simplify/improve the win32 patch, fix building with lld
The previous version of win32.patch left things in a bit more broken state
than necessary.
The previous version of the patch removed LD=gcc and removed a number of
flags, making the build trying to build a DLL (but without the option
-shared), actually producing an EXE. (The linked DLLs are later
actually removed by the contribs build system.) Instead of removing LD=gcc,
change it into LD=$(CC) which is more what glew originally intended, and
keep the flags for linking shared libraries (but remove the -soname option
which isn't supported by neither GNU ld nor lld).
This fixes building in setups where $(LD) points to lld.
Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>