Teach autoconf/configure.ac to AC_SUBST several additional values in
Makefile.config to make them available to Makefile code. These will
be useful to generate CMake package modules from the Makefile build.
Contributed by Brad King.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201052 91177308-0d34-0410-b5e6-96231b3b80d8