[all] use explicit void parameter lists

This makes it a compile-time error to call a function that semantically
takes no parameters with a nonzero number of arguments.

Previously, such code would still compile, but risk blowing up the stack
if a compiler chose to use something other than caller-cleanup calling
conventions.

client/renderers/EGL/texture.c

@@ -268,7 +268,7 @@ bool egl_texture_setup(EGL_Texture * texture, enum EGL_PixelFormat pixFmt, size_
   return true;
 }
 
-static void egl_warn_slow()
+static void egl_warn_slow(void)
 {
   static bool warnDone = false;
   if (!warnDone)