[Bug c++/83797] Inconsistent error messages for main

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83797

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Another related problem is that this should highlight the return type, not the
closing paren:

vm.cc:1:11: error: ‘::main’ must return ‘int’
 void main() { }
           ^