Export LLVM_DYLIB_COMPONENTS in LLVMConfig.cmake

Summary:
This is needed so that external projects (e.g. a standalone build of
lldb) can link to the LLVM shared library via the USE_SHARED argument of
llvm_config. Without this, llvm_config would add LLVM to the link list,
but then also add the constituent static libraries, resulting in
multiply defined symbols.

Reviewers: beanz, mgorny

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D44391

llvm-svn: 327484