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/localized/util/Imakefile

@@ -1,10 +1,13 @@
 XCOMM $XConsortium: Imakefile /main/5 1996/09/30 14:12:43 drk $
 
-SRCS = merge.c mkcatdefs.c
+DEFINES = -DNO_XLIB
+
+SRCS = merge.c mkcatdefs.c MsgCat.c
 
 all:: merge mkcatdefs
 
-NormalProgramTarget(merge,merge.o,,,)
+NormalProgramTarget(merge,merge.o MsgCat.o,,,)
 NormalProgramTarget(mkcatdefs,mkcatdefs.o,,,)
 
 DependTarget()
+LinkSourceFile(MsgCat.c,$(DTSVCSRC)/DtUtil2)