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.

(cherry picked from commit ccade50587)

test/testshader.c

@@ -228,7 +228,7 @@ static void DestroyShaderProgram(ShaderData *data)
     }
 }
 
-static SDL_bool InitShaders()
+static SDL_bool InitShaders(void)
 {
     int i;
 
@@ -282,7 +282,7 @@ static SDL_bool InitShaders()
     return SDL_TRUE;
 }
 
-static void QuitShaders()
+static void QuitShaders(void)
 {
     int i;