malloc: tcache double free check

* malloc/malloc.c (tcache_entry): Add key field.
(tcache_put): Set it.
(tcache_get): Likewise.
(_int_free): Check for double free in tcache.
* malloc/tst-tcfree1.c: New.
* malloc/tst-tcfree2.c: New.
* malloc/Makefile: Run the new tests.
* manual/probes.texi: Document memory_tcache_double_free probe.

* dlfcn/dlerror.c (check_free): Prevent double frees.

(cherry picked from commit bcdaad21)

malloc: tcache: Validate tc_idx before checking for double-frees [BZ #23907]

The previous check could read beyond the end of the tcache entry
array.  If the e->key == tcache cookie check happened to pass, this
would result in crashes.

(cherry picked from commit affec03b)