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/dthello/Imakefile

@@ -17,9 +17,10 @@ SYS_LIBRARIES = -lm -ldl -lgen
    SRCS1 = dthello.c
    SRCS = $(SRCS1)
    OBJS = dthello.o \
-          $(CDELIBSRC)/DtSvc/DtUtil2/EnvControl.o \
           $(CDELIBSRC)/DtSvc/DtUtil2/DtNlUtils.o \
-          $(CDELIBSRC)/DtSvc/DtUtil2/GetDispRes.o
+          $(CDELIBSRC)/DtSvc/DtUtil2/EnvControl.o \
+          $(CDELIBSRC)/DtSvc/DtUtil2/GetDispRes.o \
+          $(CDELIBSRC)/DtSvc/DtUtil2/MsgCat.o
 
 ComplexProgramTarget(dthello)
 

cde/programs/dthello/dthello.c

@@ -76,7 +76,7 @@
 #include <limits.h>
 #include <locale.h>
 #ifndef NO_MESSAGE_CATALOG
-# include <nl_types.h>
+# include <Dt/MsgCatP.h>
 #endif
 
 #include <Dt/EnvControlP.h>
@@ -1147,30 +1147,15 @@ GetMessage(
         int n,
         char *s )
 {
-        char *msg;
-	char *lang;
-	nl_catd catopen();
-	char *catgets();
 	static int first = 1;
-	static nl_catd nlmsg_fd;
-	if ( first ) 
+	static nl_catd nlmsg_fd = (nl_catd) -1;
+
+	if ( first )
         {
 		first = 0;
-
-		lang = (char *) getenv ("LANG");
-
-		if (!lang || !(strcmp (lang, "C"))) 
-			/*
-			 * If LANG is not set or if LANG=C, then there
-			 * is no need to open the message catalog - just
-			 * return the built-in string "s".
-			 */
-			nlmsg_fd = (nl_catd)-1;
-		else
-			nlmsg_fd = catopen("dthello", NL_CAT_LOCALE);
+		nlmsg_fd = CATOPEN("dthello", NL_CAT_LOCALE);
 	}
-	msg=catgets(nlmsg_fd,set,n,s);
-	return (msg);
+	return CATGETS(nlmsg_fd, set, n, s);
 }
 #endif