Search for Clang resources in a clang/ sibling of llvm/
Search for Clang resources in a clang/ sibling of llvm/

Some distros package LLVM and Clang resources separately with
a layout of the form

    <prefix>/lib/llvm/<major-version>/lib
    <prefix>/lib/clang/<full-version>/include

Update our search for `CLANG_RESOURCE_DIR` to support this.

Suggested-by: Gert Wollny <f358adfdcfc221868939f3e9e1fb1416dfae4e21@gmail.com>

thewtex/CastXML,CastXML/CastXML,bradking/CastXML,bradking/CastXML,ellert/CastXML,CastXML/CastXML,CastXML/CastXML,bradking/CastXML,thewtex/CastXML,ellert/CastXML,thewtex/CastXML,ellert/CastXML