[Bug preprocessor/61389] libcpp diagnostics shouldn't talk about ISO C99 for C++ input files

[3dw4rd at verizon dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61389

--- Comment #6 from Ed Smith-Rowland <3dw4rd at verizon dot net> ---
Created attachment 33085
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33085&action=edit
Basic patch for C error messages in C++

This needs building and testing (and a testcase or two).
A few existing test cases are likely to squawk also.

Also, I think
#define V(A, ...) __VA_ARGS__
void
f()
{
 V(1); // error
 V(2, ); // OK in C99?
}

I might adjust one of the comments if that's true.