The UnixCompiler class respects flags (CC, LD, AR, CFLAGS and LDFLAGS) set to the environment, whereas MSVCCompiler class does not. This change allows building CPython and any module that invokes distutils to utilize flags and executables that have been set to the environment. Inclusion of this change would ensure MSVCCompiler's behavior to be same as that of UnixCompiler and would also allow using a different set of compiler / linker / archiver, on Windows, without having the necessity for implementing separate compiler classes - using environment variables it should be possible to use a separate set of build executables - for example icl, clang, etc.