Replace AC_CHECK_INCLUDES_DEFAULT with AC_HEADER_STDC
Closes #21868 (closed)
Replace AC_CHECK_INCLUDES_DEFAULT with AC_HEADER_STDC in configure.ac.
autoconf 2.69 does not support AC_CHECK_INCLUDES_DEFAULT.
This change allows systems with the older autoconf 2.69 to successfully complete autoreconf.
Edited by David Cleaver