error message for missing function return type could be better

[Dubhead]

$ cat -n main.zig
     1	fn foo() { // missing the return type
     2	    bar();
     3	}
     4	
     5	fn bar() void {
     6	    //
     7	}
     8	
     9	pub fn main() void {
    10	    foo();
    11	}
$ zig build-exe main.zig
/home/miura/work/foo/main.zig:5:1: error: expected token '{', found 'fn'
fn bar() void {
^
$ 

Something like main.zig:1:11: error: missing type would be better.

[andrewrk]

This is #760. I'm not sure what the solution is yet.