Re: (ham/xnec2c) wanted -std=gnu17'

[Greg Troxel <gdt%lexort.com@localhost>]

C17 seems to be a corrected version of C11 and it's odd for something to
ask for it, but I can't say it's wrong.

I think it makes sense to add it.

I tried briefly  to find which version of gcc first implemented c17, and
didn't, but gcc9 doesn't seem strange and if somebody figures out a
slightly different version is the answer it is easy to fix.

Would be good to hear from somebody else who is more of a langauge lawyer..

(Yes, please keep the change the infrastructure and adjusting xnec2c
separate.)