Replace realloc with new gc_realloc function

Replace realloc with new gc_realloc function

The realloc logic has the problem that it relies on the memory being
deallocated by uninit_options rather than by freeing the gc. This
does not always happen in all code path. Especially the crypto selftest
run by make check will not call uninit_options.

This introduces a gc_realloc function that ensures that the pointer is
instead freed when gc_free is called.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20221227140249.3524943-2-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25829.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit e7f2169772f90f9bf158a17f5656a6a985e74e31)