Prune Redundant libdeps in CMake's target_link_libraries and LLVMBuild.txt.

I checked this with Release+Asserts on x86_64-mingw32. Please restore partially if this were overkill.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213064 91177308-0d34-0410-b5e6-96231b3b80d8