--enable-gcc-warnings is broken on Fedora 21 by GnuTLS code

[Dmitry Antipov]

On Fedora 21 with gnutls 3.3.10:

../../emacs/src/gnutls.c: In function ‘emacs_gnutls_global_init’:
../../emacs/src/gnutls.c:1115:7: error: ‘gnutls_global_set_mem_functions’ is 
deprecated (declared at /usr/include/gnutls/compat.h:398) 
[-Werror=deprecated-declarations]
       fn_gnutls_global_set_mem_functions (xmalloc, xmalloc, NULL,

'man gnutls_global_set_mem_functions' explicitly states that "since 3.3.0 it
is no longer possible to replace the internally used memory allocation 
functions".

I'm just curious how to hook Emacs' xmalloc/xrealloc/xfree into GnuTLS without 
that.

Dmitry