[ubsan] Merge ubsan_standalone_cxx shared library.

Summary:
Link everything, including the C++ bits, in the single
ubsan_standalone SHARED library. This matches ASan setup.

Reviewers: vitalybuka

Subscribers: kubamracek, llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D38340

llvm-svn: 314369