Okay, my original question has already been answered, by @HolyBlackCat above...
After applying his solution <--sysroot> , I now get a more-effective result:

D:\SourceCode\Git\snippets Yes, Master?? > clang++ --sysroot=c:\tdm32 prime64.cpp
prime64.cpp:77:10: error: use of undeclared identifier 'gets'
   77 |          gets(tempstr) ;   //lint !e421  dangerous function
      |          ^
1 error generated.

The one error that I'm getting now, is a separate issue, so I will address this in a separate question, though first I am going to try a couple of other things...

Thank you all for your assistance.