configure.ac: add --disable-docs option to disable doc building

Using this option to configure will disable the building of the dthelp
and dtinfo documentation files.

cde/Makefile.am

@@ -9,5 +9,9 @@ MAINTAINERCLEANFILES = Makefile.in \
 		config.h.in \
 		install-sh
 
-SUBDIRS = util lib programs include doc
+SUBDIRS = util lib programs include
+
+if BUILD_DOCS
+SUBDIRS += doc
+endif
 

cde/configure.ac

@@ -259,6 +259,13 @@ AC_ARG_ENABLE([misc-fixed],
 )
 AM_CONDITIONAL([MISC_FIXED], [test -n "$enable_misc_fixed"])
 
+dnl Build the help and dtinfo docs?
+AC_ARG_ENABLE([docs],
+        AS_HELP_STRING([--disable-docs], [Disable building help/dtinfo docs (default=no)]),
+        [disable_docs="yes"], [disable_docs=""]
+)
+AM_CONDITIONAL([BUILD_DOCS], [test -z "$disable_docs"])
+
 dnl hmmm...
 RM="rm -f"
 AC_SUBST(RM)