Convert test_* macros to tt_* macros

I'm rebasing andrea's patch from #9262 (moved) and I'm updating it to use test_eq_ptr() rather than test_eq() when comparing function pointers.

But in git commit 31f6806aa I see Nick picking tt_ptr_op(v, ==, NULL); rather than test_eq_ptr(v, NULL);.

Is this a style thing? Should we try to be more uniform?