[libFuzzer] Update Darwin test

Support for -fsanitize-coverage=trace-pc[-guard] was removed from
libFuzzer, which makes this currently fail.

This commit aligns this Darwin-specific test with its Linux counterpart
which changed in this commit:
https://github.com/llvm/llvm-project/commit/3a94519a777b9ac407a1d5ff5c31ec48b3768eec

llvm-svn: 352721