Require support for GCC 7

[JieRen98]

Hi,

GCC 7 does not have header charconv, could you add some macro for supporting the earlier compilers?

Best regards, Jie

[skrobinson]

argparse is a C++17 project and GCC 7 does not fully support C++17. My preference is to not add complexity to extend support back to older compilers. You could use argparge v2.1 or earlier to avoid the need for the charconv header.

Out of curiosity, what platform are you using that does not support GCC > v7 and has a command line interface?

[ndevenish]

For me: Intel's DPC++ SYCL compiler. The drivers for the FPGA hardware we are targeting only support Red Hat 7, and the intel toolchain requires an underlying GCC 7.4 to run on that OS.

Still, I expect that using v2.1 should be sufficient for our case.

[tdakhran]

I can confirm that v2.1 builds on

$ lsb_release -d
Description:	Ubuntu 18.04.6 LTS
$ g++ --version | head -n 1
g++ (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0

[weiqishen]

You can replace charconv with other open source implementation such as mscharconv