mach: improve compatibility with self-hosted compiler

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/engine.zig

@@ -13,8 +13,8 @@ pub const module = ecs.Module(.{
 });
 
 pub fn App(
-    modules: anytype,
-    app_init: anytype, // fn (engine: *ecs.World(modules)) !void
+    comptime modules: anytype,
+    comptime app_init: anytype, // fn (engine: *ecs.World(modules)) !void
 ) type {
     // TODO: validate modules.mach is the expected type.
     // TODO: validate init has the right function signature