Disable -Wmaybe-uninitialized for total_deadline in sunrpc/clnt_udp.c.

To work around <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91691>
for RV32, we recently disabled -Wmaybe-uninitialized for some inline
functions in inet/net-internal.h, as included by sunrpc/clnt_udp.c.

The same error has now appeared with current GCC trunk for MIPS, in a
form that is located at the definition of the variable in question and
so unaffected by the disabling in inet/net-internal.h.  Thus, this
patch adds the same disabling around the definition of that variable,
to cover the MIPS case.

Tested with build-many-glibcs.py (compilers and glibcs stages) for
mips64-linux-gnu with GCC mainline.

	* sunrpc/clnt_udp.c: Include <libc-diag.h>.
	(clntudp_call): Disable -Wmaybe-uninitialized around declaration
	of total_deadline.