llvm-config: Replace with C++ version (was llvm-config-2).
 - Reapply of r144300, with lots of fixes/migration easement in between.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145449 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed