[FunctionSpecialization][nfc] Add a test for zero function entry count (#160156)
This test is a follow up to
https://github.com/llvm/llvm-project/commit/7d748a9ceb3716a216a8b586b1d31e046bdee039
which fixes an assertion crash that occurs if the profile count is 0.
Additionally, modify `profile-counts.ll` to use `update_test_checks.py`.