[libclang] Make sure we don't access past the tokens buffer while token annotation.

Also disable crash recovery using 'LIBCLANG_DISABLE_CRASH_RECOVERY' environment variable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195819 91177308-0d34-0410-b5e6-96231b3b80d8