fix error message for incorrect panic handler fn signature
fix error message for incorrect panic handler fn signature

closes #1353

raulgrell/zig,andrewrk/zig,zig-lang/zig,raulgrell/zig,Dimenus/zig,Dimenus/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,raulgrell/zig,zig-lang/zig,Dimenus/zig