don't prototype strdup() for __clang_analyzer__ case in windows builds.

Fixes:  #12948.

Author: sezero

include/SDL3/SDL_stdinc.h

@@ -5974,8 +5974,10 @@ size_t wcslcpy(wchar_t *dst, const wchar_t *src, size_t size);
 size_t wcslcat(wchar_t *dst, const wchar_t *src, size_t size);
 #endif
 
+#ifndef _WIN32
 /* strdup is not ANSI but POSIX, and its prototype might be hidden... */
 char *strdup(const char *str);
+#endif
 
 /* Starting LLVM 16, the analyser errors out if these functions do not have
    their prototype defined (clang-diagnostic-implicit-function-declaration) */