kbuild: do not build mconf & lxdialog unless needed

Due to a limitation in kbuild all objects referred
by xxx-y or xxx-objs will be build when one of
the targets needs to e build.

This caused lxdialog to be build pulling in ncurses
that is not always available.
So avoid building mconf & lxdialog unless really needed.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/kconfig/Makefile

@@ -111,11 +111,16 @@ always := dochecklxdialog
 lxdialog := lxdialog/checklist.o lxdialog/util.o lxdialog/inputbox.o
 lxdialog += lxdialog/textbox.o lxdialog/yesno.o lxdialog/menubox.o
 
-hostprogs-y	:= conf mconf qconf gconf kxgettext
 conf-objs	:= conf.o  zconf.tab.o
 mconf-objs	:= mconf.o zconf.tab.o $(lxdialog)
 kxgettext-objs	:= kxgettext.o zconf.tab.o
 
+hostprogs-y := conf qconf gconf kxgettext
+
+ifeq ($(MAKECMDGOALS),menuconfig)
+	hostprogs-y += mconf
+endif
+
 ifeq ($(MAKECMDGOALS),xconfig)
 	qconf-target := 1
 endif