Add testing stuff to CMake documents.

  - Note "GnuWin32".
  - Note LLVM_LIT_TOOLS_DIR
  - Now we can run tests on VS w/e all tests might pass or not!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125177 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed