Clang: Fix compilation on Windows

...for LLVM snapshots (http://llvm.org/builds).

Check for lib/libclang.* if lib/clang.* is not found.

Change-Id: I6e24ac0fe696153626ded1ed3a7db85ce8d7b0f2
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: Always prefer llvm-config* from LLVM_INSTALL_DIR

Change-Id: I981c39fcbb9d17115c62cb88499c2354cffc9fa5
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: Show LLVM_LIBS and LLVM_INCLUDEPATH

Change-Id: I915a56786f29b2c6bef5b7b31a68c1a8961f241a
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>