ffi issue-0047: #run print output now routes to stdout

`#run` / post-link callback `print` output was reaching stderr via
`std.debug.print` flushes from three sites. The runtime JIT path
already writes to fd 1 (stdout) directly. Anyone redirecting one
stream saw the two halves disappear in different places.

Switches all three flush sites + the `--- build done ---` delimiter
in main.zig to `std.c.write(1, ...)` so build-time and runtime
prints share the stream the user wrote them against (they typed
the same `print(...)` at both call sites — there's no reason for
them to land on different streams). Test runner uses `2>&1` so
snapshots are unaffected; suite stays at 218/218.

Closes issue-0047.

src/ir/emit_llvm.zig

@@ -1128,9 +1128,11 @@ pub const LLVMEmitter = struct {
             var interp_inst = Interpreter.init(self.ir_mod, self.alloc);
             interp_inst.build_config = &self.build_config;
             _ = interp_inst.call(func_id, &.{}) catch {};
-            // Write comptime output to stderr (same as old comptime VM)
+            // Route #run `print` output to fd 1 so it joins the
+            // JIT-executed runtime's stream. Same call site shape as
+            // `core.flushInterpOutput` — see issue-0047.
             if (interp_inst.output.items.len > 0) {
-                std.debug.print("{s}", .{interp_inst.output.items});
+                _ = std.c.write(1, interp_inst.output.items.ptr, interp_inst.output.items.len);
             }
             interp_inst.deinit();
         }