kconfig: add build-only configurator targets

Add build-only targets for build_menuconfig, build_nconfig,
build_xconfig, and build_gconfig.
(targets must end in "config" to qualify in top-level Makefile)

This allows these target to be built without execution (e.g., to
look for errors or warnings) and/or to be built and checked by sparse.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/kconfig/Makefile

@@ -3,7 +3,8 @@
 # Kernel configuration targets
 # These targets are used from top-level makefile
 
-PHONY += xconfig gconfig menuconfig config localmodconfig localyesconfig
+PHONY += xconfig gconfig menuconfig config localmodconfig localyesconfig \
+	build_menuconfig build_nconfig build_gconfig build_xconfig
 
 ifdef KBUILD_KCONFIG
 Kconfig := $(KBUILD_KCONFIG)
@@ -33,6 +34,14 @@ config: $(obj)/conf
 nconfig: $(obj)/nconf
 	$< $(silent) $(Kconfig)
 
+build_menuconfig: $(obj)/mconf
+
+build_nconfig: $(obj)/nconf
+
+build_gconfig: $(obj)/gconf
+
+build_xconfig: $(obj)/qconf
+
 localyesconfig localmodconfig: $(obj)/conf
 	$(Q)perl $(srctree)/$(src)/streamline_config.pl --$@ $(srctree) $(Kconfig) > .tmp.config
 	$(Q)if [ -f .config ]; then 					\