When instrumenting C++ code, ubsan ends up referencing
the ubsan_type_hash_* object files, which require linking against
the C++ ABI library. When building with "clang -x c++", the code
is handled as C++, but the compiler still only links as if it was
C.
Change all cases of "%clang -x c++" into "%clangxx -x c++".
This fixes a lot of ubsan tests in mingw mode.
Differential Revision: https://reviews.llvm.org/D147687
2ce71b2c18