Fix `llvm-config` to emit the linker flag for the combined shared object built by...

Fix `llvm-config` to emit the linker flag for the combined shared object built by autoconfig/make instead of the individual components.

Summary:
This fixes `llvm-config` instead of fixing the makefiles because, AIUI, LLVM's autoconfig/make build system is on the way out anyway.

This change only affects builds that use autoconfig/make.

Reviewers: jfb

Subscribers: echristo, dschuff, llvm-commits

Differential Revision: http://reviews.llvm.org/D10716

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241938 91177308-0d34-0410-b5e6-96231b3b80d8