Fix warning for Android NDK compiler: "function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]"

https://stackoverflow.com/questions/42125/warning-error-function-declaration-isnt-a-prototype
In C int foo() and int foo(void) are different functions. int foo() accepts an arbitrary number of arguments, while int foo(void) accepts 0 arguments. In C++ they mean the same thing.

test/testgl2.c

@@ -78,7 +78,7 @@ quit(int rc)
 }
 
 static void
-Render()
+Render(void)
 {
     static float color[8][3] = {
         { 1.0, 1.0, 0.0 },