More consistently check for WIN32 instead of MSVC in CMake files

[giordano]

What does this implement/fix? Explain your changes.

With this change I was able to cross compile for Windows by using MinGW.

Any other comments?

I'm not changing them, but as far as I can tell the ifs at

rdkit/Code/MinimalLib/CMakeLists.txt

Lines 32 to 34 in 4fafb72

	if(RDK_URF_LIBS)
	list(APPEND LIBS_TO_USE RingDecomposerLib_static)
	endif()

and

rdkit/Code/MinimalLib/CMakeLists.txt

Lines 43 to 45 in 4fafb72

	if(RDK_URF_LIBS)
	list(APPEND LIBS_TO_USE RingDecomposerLib)
	endif()

are completely useless: RDK_URF_LIBS is always true, so these ifs are always hit, and RingDecomposerLib is already unconditionally added to LIBS_TO_USE at

rdkit/Code/MinimalLib/CMakeLists.txt

Line 31 in 4fafb72

SmilesParse_static GraphMol_static RingDecomposerLib_static RDGeometryLib_static RDGeneral_static )

and

rdkit/Code/MinimalLib/CMakeLists.txt

Line 42 in 4fafb72

SmilesParse GraphMol RingDecomposerLib RDGeometryLib RDGeneral )

[greglandrum]

LGTM

[greglandrum]

Thanks @giordano !