Fix format warnings when using gnu printf extensions in a setup that supports them (gcc/mingw). (#3592)

docs/CHANGELOG.txt

@@ -68,9 +68,10 @@ Other Changes:
 - InputText: Fixed updating cursor/selection position when a callback altered the buffer in a way
   where the byte count is unchanged but the decoded character count changes. (#3587) [@gqw]
 - Metrics: Fixed mishandling of ImDrawCmd::VtxOffset in wireframe mesh renderer.
-- Misc: Replaced UTF-8 decoder by branchless one by Christopher Wellons (30~40% faster). [@rokups]
+- Misc: Replaced UTF-8 decoder with one based on branchless one by Christopher Wellons. [@rokups]
   Super minor fix handling incomplete UTF-8 contents: if input does not contain enough bytes, decoder
   returns IM_UNICODE_CODEPOINT_INVALID and consume remaining bytes (vs old decoded consumed only 1 byte).
+- Misc: Fix format warnings when using gnu printf extensions in a setup that supports them (gcc/mingw). (#3592)
 - Misc: Made EndFrame() assertion for key modifiers being unchanged during the frame (added in 1.76) more
   lenient, allowing full mid-frame releases. This is to accommodate the use of mid-frame modal native
   windows calls, which leads backends such as GLFW to send key clearing events on focus loss. (#3575)

imgui.h

@@ -78,13 +78,6 @@ Index of this file:
 #include <assert.h>
 #define IM_ASSERT(_EXPR)            assert(_EXPR)                               // You can override the default assert handler by editing imconfig.h
 #endif
-#if !defined(IMGUI_USE_STB_SPRINTF) && (defined(__clang__) || defined(__GNUC__))
-#define IM_FMTARGS(FMT)             __attribute__((format(printf, FMT, FMT+1))) // To apply printf-style warnings to our functions.
-#define IM_FMTLIST(FMT)             __attribute__((format(printf, FMT, 0)))
-#else
-#define IM_FMTARGS(FMT)
-#define IM_FMTLIST(FMT)
-#endif
 #define IM_ARRAYSIZE(_ARR)          ((int)(sizeof(_ARR) / sizeof(*(_ARR))))     // Size of a static C-style array. Don't use on pointers!
 #define IM_UNUSED(_VAR)             ((void)(_VAR))                              // Used to silence "unused variable warnings". Often useful as asserts may be stripped out from final builds.
 #if (__cplusplus >= 201100)
@@ -92,6 +85,16 @@ Index of this file:
 #else
 #define IM_OFFSETOF(_TYPE,_MEMBER)  ((size_t)&(((_TYPE*)0)->_MEMBER))           // Offset of _MEMBER within _TYPE. Old style macro.
 #endif
+#if !defined(IMGUI_USE_STB_SPRINTF) && defined(__clang__)
+#define IM_FMTARGS(FMT)             __attribute__((format(printf, FMT, FMT+1)))     // Apply printf-style warnings to our formatting functions.
+#define IM_FMTLIST(FMT)             __attribute__((format(printf, FMT, 0)))
+#elif !defined(IMGUI_USE_STB_SPRINTF) && defined(__GNUC__)
+#define IM_FMTARGS(FMT)             __attribute__((format(gnu_printf, FMT, FMT+1))) // Apply printf-style warnings to our formatting functions.
+#define IM_FMTLIST(FMT)             __attribute__((format(gnu_printf, FMT, 0)))
+#else
+#define IM_FMTARGS(FMT)
+#define IM_FMTLIST(FMT)
+#endif
 
 // Warnings
 #if defined(__clang__)