llvm-shlib: Create object libraries for each component and link against them

This makes it possible to build libLLVM.so without first creating a
static library for each component.  In the case where only libLLVM.so is
built (i.e. ninja LLVM) this eliminates 150 linker jobs.

Reviewed By: stellaraccident

Differential Revision: https://reviews.llvm.org/D95727