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.

src/render/SDL_d3dmath.c

@@ -26,7 +26,7 @@
 
 /* Direct3D matrix math functions */
 
-Float4X4 MatrixIdentity()
+Float4X4 MatrixIdentity(void)
 {
     Float4X4 m;
     SDL_zero(m);

src/render/direct3d11/SDL_render_d3d11.c

@@ -808,7 +808,7 @@ done:
 
 #if defined(SDL_PLATFORM_WIN32) || defined(SDL_PLATFORM_WINGDK)
 
-static DXGI_MODE_ROTATION D3D11_GetCurrentRotation()
+static DXGI_MODE_ROTATION D3D11_GetCurrentRotation(void)
 {
     /* FIXME */
     return DXGI_MODE_ROTATION_IDENTITY;

src/render/direct3d12/SDL_render_d3d12.c

@@ -1200,7 +1200,7 @@ done:
     return result;
 }
 
-static DXGI_MODE_ROTATION D3D12_GetCurrentRotation()
+static DXGI_MODE_ROTATION D3D12_GetCurrentRotation(void)
 {
     /* FIXME */
     return DXGI_MODE_ROTATION_IDENTITY;

src/render/ps2/SDL_render_ps2.c

@@ -60,7 +60,7 @@ typedef struct
 static int vsync_sema_id = 0;
 
 /* PRIVATE METHODS */
-static int vsync_handler()
+static int vsync_handler(void)
 {
     iSignalSema(vsync_sema_id);
 

src/render/vulkan/SDL_render_vulkan.c

@@ -1639,7 +1639,7 @@ static SDL_bool VULKAN_InstanceExtensionFound(VULKAN_RenderData *rendererData, c
     return SDL_FALSE;
 }
 
-static SDL_bool VULKAN_ValidationLayersFound()
+static SDL_bool VULKAN_ValidationLayersFound(void)
 {
     uint32_t instanceLayerCount = 0;
     uint32_t i;