Clang: option generation fixes.

Change-Id: Ic876058cbd0debcc71f812b6c21215b460058968
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: do debug output depending on environment variable.

Change-Id: Id7a65fda0e1b24d9167fb055fea3f68abe21e5e1
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: disable skipped block “highlighting” through clang

The clang patch still is not in yet, so to prevent checking for the
wrong CINDEX_VERSION_MINOR, it is now disabled.

Change-Id: I914d05360551689f7c18ce1bb51ea8f4cb6947eb
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Clang: improved detection of llvm-config utility.

Now can detect llvm-config, llvm-config-3.2, llvm-config-3.3,
llvm-config-3.4 and 4 possible future versions.

Change-Id: I0ae1a75c0a0f109ff8fe2a06e256062bf017b565
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>