https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64190
--- Comment #4 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> I'm not getting this warning neither on x86_64-linux nor on i686-linux,
> otherwise I would not have committed the patch. Any information about
> the platform you are getting the warning on would be appreciated.
x86-64/Linux -m32 for me:
eric@polaris:~/build/gcc-4_9-branch/native> gcc/xgcc -Bgcc pr63551.c -m32
pr63551.c: In function 'fn2':
pr63551.c:24:9: warning: this decimal constant is unsigned only in ISO C90
union U b = { 4294967286 };
> If you can reproduce it, can you check whether providing option
> -std=c90 or something like it would suppress it?
-std=c99 works.
