Add some more C++ extensions

[velichkov]

Google C++ style guide requires .cc extension and also gcc supports few more extensions - .cxx, .CPP, c++, .cp and .C

Also improve the testing instructions in the README.md

[VictorRodriguez]

Hi @velichkov thanks a lot for the PR. I will take time to day to review and post my comments.

[ahkok]

It seems unnecessary to duplicate the same source code file 7x. Perhaps we can make a temporary copy for each iteration and use that to validate, instead. Or even symlinks?

[velichkov]

Hi @ahkok,

It seems unnecessary to duplicate the same source code file 7x.

Agree.

Perhaps we can make a temporary copy for each iteration and use that to validate, instead.

I'll try to to rework it with temporary copies.

Or even symlinks?

With symlinks it would be tricky as patch refuses to patch symlinks

File tests/max-test.cc is not a regular file -- refusing to patch
1 out of 1 hunk ignored -- saving rejects to file tests/max-test.cc.rej

and with --follow-symlinks option

patching file tests/max-test.CPP
Reversed (or previously applied) patch detected!  Assume -R? [n]

and with --follow-symlinks -f it returns 1

patching file tests/max-test.cxx
Hunk #1 FAILED at 11.
1 out of 1 hunk FAILED -- saving rejects to file tests/max-test.cxx.rej
$ echo $?
1

[VictorRodriguez]

Agree on comments from @ahkok we can make a temporary copy for each iteration. Thanks a lot for the patch !