gprofng: fix -std=gnu23 compatibility wrt unprototyped functions

gprofng: fix -std=gnu23 compatibility wrt unprototyped functions

C23 removes support for unprototyped functions. Fix function pointer types
accordingly.

This does not fix all instances, there's a few left as I commented on in
PR32374 (e.g. setitimer which I have a local workaround for but it involves
a glibc implementation detail; the Linaro precommit CI tester pointed that
out too, so dropped that).

ChangeLog:
	PR gprofng/32374

	* libcollector/collector.c (collector_sample): Fix prototype.
	* libcollector/envmgmt.c (putenv): Ditto.
	(_putenv): Ditto.
	(__collector_putenv): Ditto.
	(setenv): Ditto.
	(_setenv): Ditto.
	(__collector_setenv): Ditto.
	(unsetenv): Ditto.
	(_unsetenv): Ditto.
	(__collector_unsetenv): Ditto.
	* libcollector/jprofile.c (open_experiment): Ditto.
	(__collector_jprofile_enable_synctrace): Ditto.
	(jprof_find_asyncgetcalltrace): Ditto.
	* libcollector/libcol_util.c (__collector_util_init): Ditto.
	(ARCH): Ditto.
	* libcollector/mmaptrace.c (collector_func_load): Ditto.
	(collector_func_unload): Ditto.
	* libcollector/unwind.c (__collector_ext_unwind_init): Ditto.
	* src/collector_module.h: Ditto.