AC_PROG_CXX in autoconf 2.70

[Peter Johansson]

Hi autoconfers;

We are currently using macro
AX_CXX_COMPILE_STDCXX_11([noext], [optional])
from
http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_cxx_compile_stdcxx_11.m4

which checks if $CXX is a C++11 compiler and if not it tries with 
switches like -std=c++11. The noext macro option means that no GNU 
extension is looked for, i.e., -std=c++11 is tried rather than -std=gnu++11.

This works fine and desired with autoconf 2.69 and CXX is set to 'g++ 
-std=c++11'. If I read the code of Autoconf 2.70 correctly, it seem not 
trivial to get the same behaviour because AC_PROG_CXX sets CXX to 'g++ 
-std=gnu++11', and then when AX_CXX_COMPILE_STDCXX kicks in CXX is 
already a c++11 compiler, so it does not alter anything. Will there be a 
way to avoid the GNU extensions to be turned on?


Cheers,
Peter