Expand pseudo-components before embedding in llvm-config

Summary:
If you use pseudo-targets like AllTargetsCodeGens in LLVM_DYLIB_COMPONENTS
then a test will fail because `./bin/llvm-config --shared-mode` can't
handle these targets. We can fix this by expanding them before embedding
the string into llvm-config

Reviewers: bogner

Reviewed By: bogner

Subscribers: mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65011

llvm-svn: 366610