* elf/dl-close.c: Include stddef.h.

* elf/dl-close.c: Include stddef.h.

	(_dl_close): If called recursively, just remember GC needs to be rerun
	and decrease l_direct_opencount.  Avoid GC if l_direct_opencount
	decreased to 1.  Rerun GC at the end if any destructor unloaded some
	additional libraries.
	* elf/Makefile: Add rules to build and run unload6 test.
	* elf/unload6.c: New test.
	* elf/unload6mod1.c: New file.
	* elf/unload6mod2.c: New file.
	* elf/unload6mod3.c: New file.

	* malloc/hooks.c (mem2chunk_check): Add magic_p argument, set *magic_p
	if magic_p is not NULL.
	(top_check): Invoke MALLOC_FAILURE_ACTION if MORECORE failed.
	(malloc_check): Fail if sz == -1.
	(free_check): Adjust mem2chunk_check caller.
	(realloc_check): Likewise.  Fail if bytes == -1.  If bytes == 0 and
	oldmem != NULL, call free_check and return NULL.  If reallocating
	and returning NULL, invert magic byte again to make oldmem valid
	region for further checking.
	(memalign_check): Fail if bytes == -1.
	* malloc/Makefile: Add rules to build and run tst-mcheck.
	* malloc/tst-mcheck.c: New test.