[UBSan] Don't allow to use UBSan with anything except for ASan.

We are not able to make a reliable solution for using UBSan together
with other sanitizers with runtime support (and sanitizer_common).
Instead, we want to follow the path used for LSan: have a "standalone"
UBSan tool, and plug-in UBSan that would be explicitly embedded into
specific sanitizers (in short term, it will be only ASan).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@232829 91177308-0d34-0410-b5e6-96231b3b80d8