-# Checks for header files.
-AC_CHECK_HEADERS([limits.h stdlib.h string.h sys/acl.h unistd.h])
-
-# Checks for typedefs, structures, and compiler characteristics.
-AC_HEADER_STDBOOL
+# Predefined header checks.
+AC_HEADER_STAT # sys/stat.h
+AC_HEADER_STDBOOL # stdbool.h
+AC_HEADER_STDC # stdlib.h string.h (implied: errno.h limits.h stdio.h)