https://bugs.gentoo.org/966225
Porting to C23, lock and unlock are implicitly work on global Screen
Used include with function declaration instead of re-declaring it for
missing function.
--- a/src/gfx.c
+++ b/src/gfx.c
@@ -260,11 +260,11 @@
 
 void LinePart(Sint32 X1, Sint32 Y1, Sint32 X2, Sint32 Y2, Sint32 lower, Sint32 upper, Uint32 Color)
 {
-   lock(Screen);
+   lock();
 
    /* Draw the line */
    DoLinePart(Screen, X1, Y1, X2, Y2, lower, upper, Color, &PutPixel);
-   unlock(Screen);
+   unlock();
 }
 
 void Update()
--- a/src/joystick.c
+++ b/src/joystick.c
@@ -1,5 +1,6 @@
 #include <SDL.h>
 #include "joystick.h"
+#include "gfx.h" //for ComplainAndExit()
 
 static SDL_Joystick *joy=NULL;