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/programs/dtpdmd/nlmsg.c

@@ -34,18 +34,12 @@
  * (c) Copyright 1996 Hitachi.
  */
 
-#ifdef I18N_MSG
-
-#include <nl_types.h>
+#include "nlmsg.h"
 
 #if !defined(NL_CAT_LOCALE)
 #define NL_CAT_LOCALE 0
 #endif 
 
-#define DTPDMD_CAT_NAME "dtpdmd"
-
-#endif /* I18N_MSG */
-
 /*
  * ------------------------------------------------------------------------
  * Default message values
@@ -108,8 +102,6 @@ const char DtPdmdMsg_0015[] = "\
 
 const char DtPdmdMsg_0016[] = "%1$s: error, cannot open log file \"%2$s\". Turning off stderr message logging\n";
 
-#ifdef I18N_MSG
-
 /*
  * ------------------------------------------------------------------------
  * Name: DtPdmdGetMessage
@@ -126,26 +118,17 @@ const char DtPdmdMsg_0016[] = "%1$s: error, cannot open log file \"%2$s\". Turni
  * Returns: the string for set 'set' and number 'n'.
  */
 const char *
-DtPdmdGetMessage(
-		int set,
-		int n,
-		char * s)
+DtPdmdGetMessage(int set,
+                 int n,
+                 const char *s)
 {
-    char *msg;
-    nl_catd catopen();
-    char *catgets();
     static int first = 1;
-    static nl_catd nlmsg_fd;
-    
-    if(set == -1 || n == -1)
-	return s;
-    
-    if(first) 
+    static nl_catd nlmsg_fd = (nl_catd) -1;
+
+    if (first)
     {
 	first = 0;
-	nlmsg_fd = catopen(DTPDMD_CAT_NAME, NL_CAT_LOCALE);
+	nlmsg_fd = CATOPEN("dtpdmd", NL_CAT_LOCALE);
     }
-    msg=catgets(nlmsg_fd,set,n,s);
-    return (msg);
+    return CATGETS(nlmsg_fd, set, n, s);
 }
-#endif /* I18N_MSG */