AC_CHECK_DECLS take a comma separated list of macros/symbols,
so replace the whitespace separator with a comma.
Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>
(cherry picked from commit b715dd26572ab18fdba92f06143456c0f9d6380a)
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>