Define RtlGenRandom correctly in ntsecapi.h wrapper

Include ntsecapi.h where required and just redefine RtlGenRandom
correctly in the ntsecapi.h wrapper.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/miscfuncs.cc

@@ -8,6 +8,7 @@ details. */
 
 #include "winsup.h"
 #include "miscfuncs.h"
+#include <ntsecapi.h>
 #include <sys/uio.h>
 #include <assert.h>
 #include <alloca.h>