Move definition of _NSIG.

_NSIG is only unsed in one file, so move it there prevent redefinition
warnings reported by Kevin Brott.

defines.h

@@ -822,14 +822,6 @@ struct winsize {
 # define SSH_IOBUFSZ 8192
 #endif
 
-#ifndef _NSIG
-# ifdef NSIG
-#  define _NSIG NSIG
-# else
-#  define _NSIG 128
-# endif
-#endif
-
 /*
  * Platforms that have arc4random_uniform() and not arc4random_stir()
  * shouldn't need the latter.

openbsd-compat/readpassphrase.c

@@ -46,6 +46,14 @@
 #  define _POSIX_VDISABLE       VDISABLE
 #endif
 
+#ifndef _NSIG
+# ifdef NSIG
+#  define _NSIG NSIG
+# else
+#  define _NSIG 128
+# endif
+#endif
+
 static volatile sig_atomic_t signo[_NSIG];
 
 static void handler(int);