config: return 'no' on platforms not using msvc. add some comments to the probe.
config: return 'no' on platforms not using msvc.
add some comments to the probe.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@10504 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot