valgrind: silence invalid free in libc atexit handler

==17851== Invalid free() / delete / delete[] / realloc()
==17851==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==17851==    by 0x60BBE2B: __libc_freeres (in /lib/x86_64-linux-gnu/libc-2.19.so)
==17851==    by 0x4A256BC: _vgnU_freeres (in /usr/lib/valgrind/vgpreload_core-amd64-linux.so)
==17851==    by 0x5F8F16A: __run_exit_handlers (exit.c:97)
==17851==    by 0x5F8F1F4: exit (exit.c:104)
==17851==    by 0x5F74F4B: (below main) (libc-start.c:321)
==17851==  Address 0x63153c0 is 0 bytes inside data symbol "noai6ai_cached"

(cherry picked from commit 234443e3)

libgit2_clar.supp

@@ -62,3 +62,13 @@
 	fun:gcry_control
 	obj:*libssh2.so*
 }
+
+{
+	ignore-noai6ai_cached-double-free
+	Memcheck:Free
+	fun:free
+	fun:__libc_freeres
+	...
+	fun:exit
+	...
+}