Enable compiler checks for printf-like functions

Source/appfat.h

@@ -7,10 +7,12 @@
 
 #include <SDL.h>
 
+#include "../defs.h"
+
 namespace devilution {
 
-[[noreturn]] void app_fatal(const char *pszFmt, ...);
-void DrawDlg(const char *pszFmt, ...);
+[[noreturn]] void app_fatal(const char *pszFmt, ...) DVL_PRINTF_ATTRIBUTE(1, 2);
+void DrawDlg(const char *pszFmt, ...) DVL_PRINTF_ATTRIBUTE(1, 2);
 #ifdef _DEBUG
 [[noreturn]] void assert_fail(int nLineNo, const char *pszFile, const char *pszFail);
 #endif

SourceS/console.h

@@ -1,6 +1,8 @@
 #pragma once
 
 #if defined(_WIN64) || defined(_WIN32)
+#include "../defs.h"
+
 // Suppress definitions of `min` and `max` macros by <windows.h>:
 #define NOMINMAX 1
 #define WIN32_LEAN_AND_MEAN
@@ -8,7 +10,9 @@
 
 namespace devilution {
 
-void printInConsole(const char *fmt, ...)
+void printInConsole(const char *fmt, ...) DVL_PRINTF_ATTRIBUTE(1, 2);
+
+inline void printInConsole(const char *fmt, ...)
 {
 	static HANDLE stderrHandle = NULL;
 	if (stderrHandle == NULL) {

SourceS/sdl2_to_1_2_backports.h

@@ -10,6 +10,7 @@
 #include <cstddef>
 
 #include "console.h"
+#include "../defs.h"
 #include "../SourceX/stubs.h"
 
 #define WINDOW_ICON_NAME 0
@@ -54,6 +55,8 @@
 #define SDL_JoystickID Sint32
 #define SDL_JoystickNameForIndex SDL_JoystickName
 
+void SDL_Log(const char *fmt, ...) DVL_PRINTF_ATTRIBUTE(1, 2);
+
 inline void SDL_Log(const char *fmt, ...)
 {
 	char message[256];

defs.h

@@ -203,3 +203,10 @@
 #else
 #define DVL_ATTRIBUTE_ALWAYS_INLINE
 #endif
+
+#if DVL_HAVE_ATTRIBUTE(format) || (defined(__GNUC__) && !defined(__clang__))
+#define DVL_PRINTF_ATTRIBUTE(fmtargnum, firstarg) \
+  __attribute__((__format__(__printf__, fmtargnum, firstarg)))
+#else
+#define DVL_PRINTF_ATTRIBUTE(fmtargnum)
+#endif