Fix warning: strict prototypes (#14992)

clang: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]

src/core/unix/SDL_gtk.c

@@ -78,7 +78,7 @@ static void QuitGtk(void)
     libgtk = NULL;
 }
 
-static bool IsGtkInit()
+static bool IsGtkInit(void)
 {
     return libgdk != NULL && libgtk != NULL;
 }

src/tray/windows/SDL_tray.c

@@ -226,7 +226,7 @@ static wchar_t *escape_label(const char *in)
     return out;
 }
 
-static HICON load_default_icon()
+static HICON load_default_icon(void)
 {
     HINSTANCE hInstance = GetModuleHandle(NULL);
     if (!hInstance) {

src/video/openvr/SDL_openvrvideo.c

@@ -74,7 +74,7 @@ SDL_ELF_NOTE_DLOPEN(
 // For access to functions that don't get the video data context.
 SDL_VideoData * global_openvr_driver;
 
-static void InitializeMouseFunctions();
+static void InitializeMouseFunctions(void);
 
 struct SDL_CursorData
 {
@@ -92,9 +92,9 @@ static void (APIENTRY *ov_glRenderbufferStorage)(GLenum target, GLenum internalf
 static void (APIENTRY *ov_glFramebufferRenderbuffer)(GLenum target, GLenum attachment, GLenum renderbuffertarget, GLuint renderbuffer);
 static void (APIENTRY *ov_glFramebufferTexture2D)(GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level);
 static GLenum (APIENTRY *ov_glCheckNamedFramebufferStatus)(GLuint framebuffer, GLenum target);
-static GLenum (APIENTRY *ov_glGetError)();
-static void (APIENTRY *ov_glFlush)();
-static void (APIENTRY *ov_glFinish)();
+static GLenum (APIENTRY *ov_glGetError)(void);
+static void (APIENTRY *ov_glFlush)(void);
+static void (APIENTRY *ov_glFinish)(void);
 static void (APIENTRY *ov_glGenTextures)(GLsizei n, GLuint *textures);
 static void (APIENTRY *ov_glDeleteTextures)(GLsizei n, GLuint *textures);
 static void (APIENTRY *ov_glTexParameterf)(GLenum target, GLenum pname, GLfloat param);
@@ -1431,7 +1431,7 @@ static bool OPENVR_ShowMessageBox(SDL_VideoDevice *_this,const SDL_MessageBoxDat
     return true;
 }
 
-static void InitializeMouseFunctions()
+static void InitializeMouseFunctions(void)
 {
     SDL_Mouse *mouse = SDL_GetMouse();
     mouse->CreateCursor = OPENVR_CreateCursor;

src/video/windows/SDL_windowsclipboard.c

@@ -33,7 +33,7 @@
 // Assume we can directly read and write BMP fields without byte swapping
 SDL_COMPILE_TIME_ASSERT(verify_byte_order, SDL_BYTEORDER == SDL_LIL_ENDIAN);
 
-static UINT GetClipboardFormatPNG()
+static UINT GetClipboardFormatPNG(void)
 {
     static UINT format;
 

src/video/windows/SDL_windowskeyboard.c

@@ -101,7 +101,7 @@ static void WIN_CacheKeymap(HKL layout, SDL_Keymap *keymap)
     ++keymap_cache_size;
 }
 
-static SDL_Keymap *WIN_BuildKeymap()
+static SDL_Keymap *WIN_BuildKeymap(void)
 {
     SDL_Scancode scancode;
     BYTE keyboardState[256] = { 0 };

src/video/x11/SDL_x11xinput2.c

@@ -139,7 +139,7 @@ static SDL_Window *xinput2_get_sdlwindow(SDL_VideoData *videodata, Window window
 }
 
 #ifdef SDL_VIDEO_DRIVER_X11_XINPUT2_SUPPORTS_SCROLLINFO
-static void xinput2_reset_scrollable_valuators()
+static void xinput2_reset_scrollable_valuators(void)
 {
     for (int i = 0; i < scrollable_device_count; ++i) {
         for (int j = 0; j < scrollable_devices[i].scroll_info_count; ++j) {

test/testpalette.c

@@ -304,7 +304,7 @@ static SDL_Texture *CreateTexture(const void *pixels, int pitch)
     return tex;
 }
 
-static bool CreateTextures()
+static bool CreateTextures(void)
 {
     Uint8 data[256];
     int i;