Use a relaxed substring check for function names in a test

The TestTailCallFrameSBAPI.py test checks that function names in a
backtrace are equal to an expected value.

Use a relaxed substring check because function dislpay names are
platform-dependent. E.g we see "void sink(void)" on Windows, but "sink()" on
Darwin. This seems like a bug -- just work around it for now.

llvm-svn: 344634