c63ab13a9e
In cases where we build ROOT with -Dbuiltin_llvm=Off -Dbuiltin_clang=On and we have installed both llvm and clang in /usr/ clad will pick up the clang headers from there too. This patch gives higher priority to the header files which ROOT is supposed to use. It fixes a very obscure initialization issue due to different versions of the ASTContext.h installed and used by ROOT.