pragma change breaks build

[David Miller]

This change:

2015-04-19  Paul Eggert  <eggert@cs.ucla.edu>

        * stdlib/setenv.c (__add_to_environ):
        Dump core quickly if setenv (..., NULL, ...) is called.
        This time, do it the right way, and pacify GCC with a pragma.

Breaks, rather than fixes, the build for me.  I don't think we can
universally assume that this pragma facility is available:

setenv.c:27:9: error: unknown option after ‘#pragma GCC diagnostic’ kind [-Werror=pragmas]
setenv.c:27:9: error: unknown option after ‘#pragma GCC diagnostic’ kind [-Werror=pragmas]

Why don't we use something that works regardless of GCC version, such
as modifying the cflags on a per-target basis in the appropriate
Makefile?

Thanks.