MINOR: pools: use mallinfo2() when available instead of mallinfo()

MINOR: pools: use mallinfo2() when available instead of mallinfo()

Ilya reported in issue #1391 a build warning on Fedora about mallinfo()
being deprecated in favor of mallinfo2() since glibc-2.33. Let's add
support for it. This should be backported where the following commit is
also backported: 157e39303 ("MINOR: pools: automatically disable
malloc_trim() with external allocators").

(cherry picked from commit c2afb860f297eb82039d821bd25bdd3cf66abe28)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 3bf75694c2ba89c1b705ce94b5543aa30fccf4a7)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>