[libclang] Introduce clang_Location_isInSystemHeader to check if a location resides in a system header.

This is a modified patch provided from Mikołaj Siedlarek!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179384 91177308-0d34-0410-b5e6-96231b3b80d8
Disable following tests for Hexagon:

1) Driver/output-file-is-dir.c - Checks for object file which can't
be created for Hexagon since assembler is unavailable.
2) PCH/cxx-typeid.cpp - 'typeinfo' include file is unavailable for Hexagon.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179385 91177308-0d34-0410-b5e6-96231b3b80d8