cmdutils: check for SetDllDirectory() availability

It's only available on Windows XP or newer.

Should fix compilation with mingw32 using the default OS target.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: James Almer <jamrial@gmail.com>

cmdutils.c

@@ -113,7 +113,7 @@ static void log_callback_report(void *ptr, int level, const char *fmt, va_list v
 
 void init_dynload(void)
 {
-#ifdef _WIN32
+#if HAVE_SETDLLDIRECTORY
     /* Calling SetDllDirectory with the empty string (but not NULL) removes the
      * current working directory from the DLL search path as a security pre-caution. */
     SetDllDirectory("");

configure

@@ -1728,6 +1728,7 @@ SYSTEM_FUNCS="
     pthread_cancel
     sched_getaffinity
     SetConsoleTextAttribute
+    SetDllDirectory
     setmode
     setrlimit
     Sleep
@@ -4708,6 +4709,7 @@ check_func_headers windows.h GetSystemTimeAsFileTime
 check_func_headers windows.h MapViewOfFile
 check_func_headers windows.h PeekNamedPipe
 check_func_headers windows.h SetConsoleTextAttribute
+check_func_headers windows.h SetDllDirectory
 check_func_headers windows.h Sleep
 check_func_headers windows.h VirtualAlloc
 check_func_headers glob.h glob