prevent recursion in %_defconfig rules

Signed-off-by: Jérémy Rosen <jeremy.rosen@openwide.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -761,10 +761,14 @@ defconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< --defconfig=$(TOPDIR)/configs/$@ $(CONFIG_CONFIG_IN)
 
+$(TOPDIR)/configs/%_defconfig:;
+
 %_defconfig: $(BUILD_DIR)/buildroot-config/conf $(BR2_EXTERNAL)/configs/%_defconfig outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< --defconfig=$(BR2_EXTERNAL)/configs/$@ $(CONFIG_CONFIG_IN)
 
+$(BR2_EXTERNAL)/configs/%_defconfig:;
+
 savedefconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
 	@mkdir -p $(BUILD_DIR)/buildroot-config
 	@$(COMMON_CONFIG_ENV) $< \