Have llvm-c-test only use libLLVM if libLLVM has all the right components.

Summary: We should only have llvm-c-test use libLLVM if the library is built with the default set of components or if LLVM_DYLIB_COMPONENTS includes all the LLVM_LINK_COMPONENTS required for llvm-c-test. Making libLLVM always used causes build failures if libLLVM doesn't include all

Reviewers: chapuni, ributzka

Reviewed By: ributzka

Subscribers: ributzka, llvm-commits

Differential Revision: http://reviews.llvm.org/D6668