[Bug c/55976] -Werror=return-type should error on returning a value from a void function

[dave.pagan at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55976

--- Comment #12 from Dave Pagan <dave.pagan at oracle dot com> ---
New test pr55976-1.c is failing due to unaccounted for extraneous output from
the compiler. Test requires addition of dg-prune-output. Adding the directive
and will send patch shortly.