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

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

llvm-svn: 241938