Ideally would want to enable -DNeedFunctionPrototypes=1
but it leads to more issues not handled here.

https://bugs.gentoo.org/870412
--- a/eyedude.c
+++ b/eyedude.c
@@ -51,2 +51,3 @@
 #include <stdio.h>
+#include <stdlib.h>
 #include <math.h>
--- a/include/intro.h
+++ b/include/intro.h
@@ -84,2 +84,3 @@
 void DrawIntroTitle(Display *display, Window window, int x, int y);
+void HandleBlink(Display *display, Window window);
 #else
@@ -92,2 +93,3 @@
 void DoIntroTitle();
+void HandleBlink();
 #endif
--- a/include/level.h
+++ b/include/level.h
@@ -74,2 +74,3 @@
 void DisplayLevelInfo(Display *display, Window window, u_long level);
+void DisplayLevelNumber(Display *display, Window window, u_long level);
 void CheckGameRules(Display *display, Window window);
@@ -113,2 +114,3 @@
 void DisplayLevelInfo();
+void DisplayLevelNumber();
 void CheckGameRules();
--- a/main.c
+++ b/main.c
@@ -231,3 +231,3 @@
 {
-	static oldx = 0;
+	static int oldx = 0;
 	int x, y;