C_NUMERIC=C might not be necessary, but setting it doesn't hurt.

Reported-by: Simon Horman <horms@verge.net.au>
Reported-by: Sergei Trofimovich <slyfox@inbox.ru>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Tested-by: Simon Horman <horms@verge.net.au>
Tested-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
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