add_lld_library -> add_llvm_library

* Works better for shared libraries (sets PRIVATE instead of INTERFACE)
* Fixes http://llvm.org/bugs/show_bug.cgi?id=22269
* Also, use build-target names instead of component names

Differential Revision: http://reviews.llvm.org/D7074

From: Greg Fitzgerald <garious@gmail.com>
llvm-svn: 226702