SDL: stdinc: _Countof is only available in C mode

SDL Commits
1 
From 2fa7ba1e4fe54918be75a9a466b9ae51fbe14d60 Mon Sep 17 00:00:00 2001
From: Anonymous Maarten <[EMAIL REDACTED]>
Date: Thu, 14 May 2026 17:36:57 +0200
Subject: [PATCH] stdinc: _Countof is only available in C mode

---
 include/SDL3/SDL_stdinc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/SDL3/SDL_stdinc.h b/include/SDL3/SDL_stdinc.h
index 3e2266dc8f65a..893f2052f7dc2 100644
--- a/include/SDL3/SDL_stdinc.h
+++ b/include/SDL3/SDL_stdinc.h
@@ -256,7 +256,7 @@ void *alloca(size_t);
 #define SDL_arraysize(array) (sizeof(array)/sizeof(array[0]))  /* or `_Countof(array)` on recent gcc and clang */
 
 #else
-#if (defined(__GNUC__) && __GNUC__ >= 16) || SDL_HAS_EXTENSION(c_countof)
+#if !defined(__cplusplus) && ((defined(__GNUC__) && __GNUC__ >= 16) || SDL_HAS_EXTENSION(c_countof))
 #define SDL_arraysize(array) _Countof(array)
 #else
 #define SDL_arraysize(array) (sizeof(array)/sizeof(array[0]))