how to configure a c++ source build for c++11

I am trying to make and install MGSim simulator from source code. To do that I entered the following configuration command:
[root@dhcppc2 build-mtalpha]# ../configure --target=mtalpha --disable-trace-checks --prefix=/home/mehdi/mgsim CXX=g++ CPPFLAGS=-std=c++0x

I think I have enabled C++11 support by providing `c++0x' flag, but I still get the following error:

configure: error: *** A compiler with support for C++11 language features is required.

I entered other alternatives for c++0x such as c++11, g++, gnu-0x, etc. but none worked.
The full configure output can be found here here.