Centralize catgets() calls through MsgCat

CDE has relied upon catgets() implementations following a relaxed
interpretation of the XPG internationalization standard that ignored
-1, the standard error value returned by catopen, as the catalog
argument. However, this same behavior causes segmentation faults with
the musl C library.

This patch:

- Centralizes (with the exception of ToolTalk) all calls to catopen(),
  catgets(), and catclose() through MsgCat within the DtSvc library.
- Prevents calls to catgets() and catclose() that rely upon
  undefined behavior.
- Eliminates a number of bespoke catgets() wrappers, including multiple
  redundant caching implementations designed to work around a design
  peculiarity in HP/UX.
- Eases building CDE without XPG internationalization support by providing
  the appropriate macros.

cde/lib/DtSearch/msgutil.c

@@ -122,7 +122,7 @@ char           *nowstring (time_t * now)
     }
     time_ptr = _XLocaltime(now, localtime_buf);
     strftime (buf, sizeof (buf),
-	catgets (dtsearch_catd, MS_misc, 2, "%Y/%m/%d,%H:%M:%S"),
+	CATGETS(dtsearch_catd, MS_misc, 2, "%Y/%m/%d,%H:%M:%S"),
 	time_ptr);
     return buf;
 }  /* nowstring() */
@@ -342,8 +342,8 @@ void           *austext_malloc (size_t size, char *location, void *ignore)
 
     ptr = ((aa_argv0) ? aa_argv0 : "");
     if (location == NULL)
-	location = catgets (dtsearch_catd, MS_misc, 1, "<null>");
-    outofmem_msg = catgets (dtsearch_catd, MS_misc, 3,
+	location = CATGETS(dtsearch_catd, MS_misc, 1, "<null>");
+    outofmem_msg = CATGETS(dtsearch_catd, MS_misc, 3,
 	"*** %sOut of Memory at %s asking for %lu bytes! ***\n");
     fprintf (aa_stderr, outofmem_msg, ptr, location, size);
     fflush (aa_stderr);