PR18870: Parse language linkage specifiers properly if the string-literal is
spelled in an interesting way.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201536 91177308-0d34-0410-b5e6-96231b3b80d8
PR18839: 'extern "C++"' also adds an implicit 'extern', not just 'extern "C"'.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201537 91177308-0d34-0410-b5e6-96231b3b80d8