AC_USE_SYSTEM_EXTENSIONS
AC_SYS_LARGEFILE
AC_PROG_CC
-AC_PROG_CC_STDC
+# AC_PROG_CC_STDC was merged in AC_PROG_CC in autoconf 2.70
+m4_version_prereq([2.70], [], [AC_PROG_CC_STDC])
AC_PROG_CXX
RW_PROG_CXX_WORKS
AM_CONDITIONAL([CXX_WORKS], [test "x$rw_cv_prog_cxx_works" = "xyes"])