[libclang] Add some constness in CXSourceLocation and CXSourceRange.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172261 91177308-0d34-0410-b5e6-96231b3b80d8
[PCH] Make the const_cast explicit to silence a compiler warning.

Patch by David Greene.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172262 91177308-0d34-0410-b5e6-96231b3b80d8