fix autoconf build from r133710

Sorry! This commit worked in CMake, but
CXX_INCLUDE_ROOT is defined in a different
config.h for autoconf.




git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133715 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed