ld testsuite function pointer comparisons vs. hppa

ld testsuite function pointer comparisons vs. hppa

ld/testsuite/ld-elf/check-ptr-eq.c fails for hppa, since function
pointers may point at plabels.  It isn't valid to cast two function
pointers to void* and then compare the void pointers.

	* testsuite/ld-elf/check-ptr-eq.c (check_ptr_eq): Change params
	from void pointers to function pointers.
	* testsuite/ld-elf/pr18718.c: Update to suit.
	* testsuite/ld-elf/pr18720a.c: Update to suit.