[UBSan] Don't link UBSan runtime into shared libraries.

It used to be a feature of UBSan (it could sanitize a standalone
shared object instead of the whole program), but now it causes
more problems, like PR20165.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212064 91177308-0d34-0410-b5e6-96231b3b80d8