Fix clang frontend for python 3
Merge branch 'fix-clang-py3' of github.com:girving/xdress into girving-fix-clang-py3
Merge branch 'clang' of github.com:xdress/xdress into girving-fix-clang-py3
Fix clang frontend for python 3

libclang synced from https://github.com/xdress/clang/commit/ba12a91830c6335a594ac7aa4f0f676206732356.
Merge branch 'fix-clang-py3' of github.com:girving/xdress into girving-fix-clang-py3
Fix libclang segfaults for undefined classes

libclang synced from https://github.com/xdress/clang/commit/42a03caec23de044db49bf75ef8285e1401c576f.