[ccan] Annoying warning, a.k.a. how to add to CFLAGS

[Ian Zimmerman]

When I checkout current master, run ./tools/configurator/configurator >
config.h and then make, I get exactly 1 warning for the whole thing:

ccan/strgrp/strgrp.c: In function ‘grp_for’:
ccan/strgrp/strgrp.c:296:0: warning: ignoring #pragma omp parallel [-Wunknown-pragmas]
     #pragma omp parallel for schedule(dynamic)

I figured out that I can silence that by adding -fopenmp to my CFLAGS.
But how to do that permanently?  I don't want to specify that on the
command line every time, and I also don't want to set it in the
environment because sometimes I compile other things than ccan ;-)

Is there a reason why this is not in the master Makefile?

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