Cygwin: kill(1): don't print spurious error message

Make kill -V and kill -l exit immediately, thus stopping to
print "not enough arguments" accidentally.

Fixes: ef48a2cad3 ("* kill.cc (prog_name) New global variable.")
Fixes: c49fa76263 ("* Makefile.in (kill.exe): Add as a specific target.")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/release/3.4.7

@@ -1,5 +1,8 @@
 Bug Fixes
 ---------
 
-Fix CPU_SET(3) macro type mismatch by making the macros type-safe.
-Addresses https://cygwin.com/pipermail/cygwin/2023-March/253220.html
+- Fix CPU_SET(3) macro type mismatch by making the macros type-safe.
+  Addresses https://cygwin.com/pipermail/cygwin/2023-March/253220.html
+
+- kill(1): don't print spurious error message.
+  Addresses: https://cygwin.com/pipermail/cygwin/2023-March/253291.html

winsup/utils/kill.cc

@@ -65,6 +65,7 @@ print_version ()
 	  CYGWIN_VERSION_DLL_MAJOR % 1000,
 	  CYGWIN_VERSION_DLL_MINOR,
 	  strrchr (__DATE__, ' ') + 1);
+  exit (0);
 }
 
 static const char *
@@ -126,6 +127,7 @@ listsig (const char *in_sig)
       else
 	printf ("%d\n", sig);
     }
+  exit (0);
 }
 
 static void