fixed compileError printing

exercises/074_comptime9.zig

@@ -1,4 +1,5 @@
-const print = @import("std").debug.print;
+const std = @import("std");
+const print = std.debug.print;
 
 // We're going to (ab)use the power of Zig to make animal hybrid creatures!
 // What do you think a GatorMouse would look like?  Eek.
@@ -58,7 +59,7 @@ fn makeCreature(comptime count: usize, comptime fmt: []const u8) [count]Animal {
                 // other animals or is this an error?
                 'g' => ???,
 
-                else => @compileError("No animal starts with '" ++ char ++ "'!"),
+                else => @compileError(std.fmt.comptimePrint("No animal starts with '{c}'!", .{char})),
             },
 
             .l => switch (char) {