std-gnu11: Support Autoconf versions < 2.64

[Bruno Haible]

While testing with Autoconf 2.63, I noticed this error:

$ autoconf 
configure:5805: error: possibly undefined macro: _AC_DO_LIMIT
      If this token and others are legitimate, please use m4_pattern_allow.
      See the Autoconf documentation.
configure:5805: error: possibly undefined macro: AS_MESSAGE_LOG_FD

This patch fixes it.


2018-10-22  Bruno Haible  <br...@clisp.org>

        std-gnu11: Support Autoconf versions < 2.64.
        * m4/std-gnu11.m4 (AC_PROG_CC, AC_PROG_CXX): Use _AC_DO as fallback
        when _AC_DO_LIMIT does not exist.

diff --git a/m4/std-gnu11.m4 b/m4/std-gnu11.m4
index c85ac43..bae4ed1 100644
--- a/m4/std-gnu11.m4
+++ b/m4/std-gnu11.m4
@@ -70,7 +70,7 @@ _AS_ECHO_LOG([checking for _AC_LANG compiler version])
 set X $ac_compile
 ac_compiler=$[2]
 for ac_option in --version -v -V -qversion -version; do
-  _AC_DO_LIMIT([$ac_compiler $ac_option >&AS_MESSAGE_LOG_FD])
+  m4_ifdef([_AC_DO_LIMIT],[_AC_DO_LIMIT],[_AC_DO])([$ac_compiler $ac_option 
>&AS_MESSAGE_LOG_FD])
 done
 
 m4_expand_once([_AC_COMPILER_EXEEXT])[]dnl
@@ -135,7 +135,7 @@ _AS_ECHO_LOG([checking for _AC_LANG compiler version])
 set X $ac_compile
 ac_compiler=$[2]
 for ac_option in --version -v -V -qversion; do
-  _AC_DO_LIMIT([$ac_compiler $ac_option >&AS_MESSAGE_LOG_FD])
+  m4_ifdef([_AC_DO_LIMIT],[_AC_DO_LIMIT],[_AC_DO])([$ac_compiler $ac_option 
>&AS_MESSAGE_LOG_FD])
 done
 
 m4_expand_once([_AC_COMPILER_EXEEXT])[]dnl