[Apple Clang] Expose llvm-config from stage2 builds in stage1

This exposes the stage2-llvm-config target though the stage1 build configuration.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@264125 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/caches/Apple-stage1.cmake

@@ -37,6 +37,7 @@ set(CLANG_BOOTSTRAP_TARGETS
   check-all
   check-llvm
   check-clang
+  llvm-config
   test-suite
   test-depends
   llvm-test-depends