create autoconf test that checks for too old g++ STL in combination with icpc

Compilation of the ET on clusters regularly fails if icpc is combined with a too old STL from g++. As of https://www.einsteintoolkit.org/about/releases/ET_2022_05_announcement.html the ET must be compiled with STL from gcc-6 (or later) when using icpc to provide for full C++11 support (and not technical preview C++11).

Similarly before, using gcc-4.3 (default on some redhat systems) will fail to compile vectors due to bad default constructors.

We should construct an autoconf test that tests for these issues and reports a useful error message to users setting up Cactus / the ET on their cluster. Note that technically Cactus would work with older C++ compilers but the Einstein Toolkit will not.

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