do not tailcall __sanitizer_cov_trace_pc [PR90746]

When instrumentation is requested via -fsanitize-coverage=trace-pc, GCC
emits calls of __sanitizer_cov_trace_pc callback in each basic block.
This callback is supposed to be implemented by the user, and should be
able to identify the containing basic block by inspecting its return
address. Tailcalling the callback prevents that, so disallow it.

gcc/ChangeLog:

	PR sanitizer/90746
	* calls.cc (can_implement_as_sibling_call_p): Reject calls
	to __sanitizer_cov_trace_pc.

gcc/testsuite/ChangeLog:

	PR sanitizer/90746
	* gcc.dg/sancov/basic0.c: Verify absence of tailcall.