Revert "[cmake][msvc] Enable standards-conforming preprocessor"

This reverts commit 12d8e7c6.

The Windows MLIR buildbot started failing with:

C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\winbase.h(9531): error C2220: the following warning is treated as an error
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\winbase.h(9531): warning C5105: macro expansion producing 'defined' has undefined behavior
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\winbase.h(9531): note: to simplify migration, consider the temporary use of /Wv:18 flag with the version of the compiler with which you used to build without warnings