[compiler-rt][asan][test] Fix lit test config on MinGW

MinGW is GCC-like and does not support clang-cl, so clean up the lit cfg
to reflect that. Also mark all Windows test cases using clang-cl as
UNSUPPORTED for now. We should probably adapt most of these test cases
to use the GCC-like clang driver, but that will be for later.

Differential Revision: https://reviews.llvm.org/D147057