Use SIGCHLD rather than SIGCLD.

Patch from Pascal Stumpf <Pascal.Stumpf@cubes.de>

The official POSIX name for this signal is SIGCHLD.  Linux probably
has SIGCLD only for SysV compatibility, but BSD does not.

cde/programs/dtpad/main.c

@@ -985,7 +985,7 @@ InitEditSessionAndFirstPad(
         sigfillset(&act.sa_mask);
         act.sa_flags = 0;
         act.sa_handler = SigcldHndlr;
-        sigaction(SIGCLD, &act, (struct sigaction *)NULL);
+        sigaction(SIGCHLD, &act, (struct sigaction *)NULL);
     }
 }
 
@@ -1591,7 +1591,7 @@ void SigcldHndlr (int dummy)
     /*
      * Is this really necessary?
      */
-    sigaction(SIGCLD, &act, (struct sigaction *)NULL);
+    sigaction(SIGCHLD, &act, (struct sigaction *)NULL);
 }