libgcov: fix TOPN type casting

libgcov: fix TOPN type casting

The patch fixes tree-prof.exp tests on solaris11 and i686-linux-gnu,
problem was that sizeof of a pointer is different from sizeof gcov_type.

I'm going to install it if there are no objections.
Thanks,
Martin

libgcc/ChangeLog:

	PR gcov-profile/95494
	* libgcov-driver.c (write_top_counters): Cast first to
	intptr_t as sizeof(*) != sizeof(gcov_type).
	* libgcov.h (gcov_counter_set_if_null): Remove.
	(gcov_topn_add_value): Cast first to intptr_t and update
	linked list directly.