dnl This is because Autoconf default includes check for STDC_HEADERS,
dnl HAVE_SYS_TYPES_H, etc. before including them.
AC_HEADER_STDC
+AC_HEADER_STDBOOL
AC_CHECK_HEADERS(sys/types.h sys/stat.h)
dnl Now check for the others.
AC_CHECK_HEADERS(string.h strings.h limits.h unistd.h sys/time.h)