gprofng: fix build with -std=gnu23

gprofng: fix build with -std=gnu23

Fix function pointer types accordingly.
Remove unused function pointers.

gprofng/ChangeLog
2024-11-21  Vladimir Mezentsev  <vladimir.mezentsev@oracle.com>

	PR gprofng/32374
	PR gprofng/32373
	* common/cpuid.c: Define ATTRIBUTE_UNUSED if necessary.
	* libcollector/libcol_util.c (sysinfo): Remove unused pointer.
	* src/collector_module.h: Likewise.
	* libcollector/dispatcher.c (setitimer): Fix prototype.
	* libcollector/linetrace.c (system, grantpt, ptsname): Likewise.
	* testsuite/gprofng.display/mttest/mttest.c (dump_arrays): Likewise.
	* testsuite/gprofng.display/synprog/endcases.c (xinline_code,
	s_inline_code): Likewise.
	* testsuite/gprofng.display/synprog/inc_inline.h (ext_inline_code):
	Likewise.
	* testsuite/gprofng.display/synprog/synprog.c (doabort): Rename nullptr.