Enable linker garbage collection for the PRU target.

bfd	* elf32-pru.c (elf_backend_can_gc_sections): Define as 1.

ld	* testsuite/ld-elf/group8a.d: Remove pru from XFAIL list.
	* testsuite/ld-elf/group8b.d: Ditto.
	* testsuite/ld-elf/group9a.d: Ditto.
	* testsuite/ld-elf/group9b.d: Ditto.
	* testsuite/ld-elf/pr12851.d: Ditto.
	* testsuite/ld-elf/pr22677.d: Ditto.
	* testsuite/lib/ld-lib.exp (check_gc_sections_available): Remove
	pru from list.