linux: add support for linux26-{menuconfig,xconfig,gconfig} targets

These targets allow the user to customize the configuration of the
Linux kernel. After changing the kernel configuration, the next time
the user runs "make", the kernel is rebuilt to take into account the
new configuration (not rebuilt from scratch).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

linux/linux.mk

@@ -98,8 +98,9 @@ endif
 	$(TARGET_MAKE_ENV) $(MAKE) $(LINUX26_MAKE_FLAGS) -C $(@D) oldconfig
 	$(Q)touch $@
 
-# Compilation
-$(LINUX26_DIR)/.stamp_compiled: $(LINUX26_DIR)/.stamp_configured
+# Compilation. We make sure the kernel gets rebuilt when the
+# configuration has changed.
+$(LINUX26_DIR)/.stamp_compiled: $(LINUX26_DIR)/.stamp_configured $(LINUX26_DIR)/.config
 	@$(call MESSAGE,"Compiling kernel")
 	$(TARGET_MAKE_ENV) $(MAKE) $(LINUX26_MAKE_FLAGS) -C $(@D) $(LINUX26_IMAGE_NAME)
 	@if [ $(shell grep -c "CONFIG_MODULES=y" $(LINUX26_DIR)/.config) != 0 ] ; then 	\
@@ -123,6 +124,9 @@ $(LINUX26_DIR)/.stamp_installed: $(LINUX26_DIR)/.stamp_compiled
 
 linux26: host-module-init-tools $(LINUX26_DEPENDENCIES) $(LINUX26_DIR)/.stamp_installed
 
+linux26-menuconfig linux26-xconfig linux26-gconfig: $(LINUX26_DIR)/.stamp_configured
+	$(MAKE) $(LINUX26_MAKE_FLAGS) -C $(LINUX26_DIR) $(subst linux26-,,$@)
+
 ifeq ($(BR2_LINUX_KERNEL),y)
 TARGETS+=linux26
 endif