build: add option to treat recursive deps as error

Running make with RECURSIVE_DEP_IS_ERROR=1 will cause a hard failure
when a recursive dependency is detected.  This is useful to apply
stricter Ci tests, for example.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

include/toplevel.mk

@@ -99,6 +99,9 @@ prepare-tmpinfo: FORCE
 		$(_SINGLE)$(NO_TRACE_MAKE) menuconfig $(PREP_MK); \
 	fi
 
+ifeq ($(RECURSIVE_DEP_IS_ERROR),1)
+  KCONF_FLAGS=--fatalrecursive
+endif
 ifneq ($(DISTRO_PKG_CONFIG),)
 scripts/config/%onf: export PATH:=$(dir $(DISTRO_PKG_CONFIG)):$(PATH)
 endif
@@ -111,7 +114,7 @@ $(eval $(call rdep,scripts/config,scripts/config/mconf))
 
 config: scripts/config/conf prepare-tmpinfo FORCE
 	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
-		$< Config.in
+		$< $(KCONF_FLAGS) Config.in
 
 config-clean: FORCE
 	$(_SINGLE)$(NO_TRACE_MAKE) -C scripts/config clean
@@ -120,7 +123,7 @@ defconfig: scripts/config/conf prepare-tmpinfo FORCE
 	touch .config
 	@if [ ! -s .config -a -e $(HOME)/.openwrt/defconfig ]; then cp $(HOME)/.openwrt/defconfig .config; fi
 	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
-		$< --defconfig=.config Config.in
+		$< $(KCONF_FLAGS) --defconfig=.config Config.in
 
 confdefault-y=allyes
 confdefault-m=allmod
@@ -129,7 +132,7 @@ confdefault:=$(confdefault-$(CONFDEFAULT))
 
 oldconfig: scripts/config/conf prepare-tmpinfo FORCE
 	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
-		$< --$(if $(confdefault),$(confdefault),old)config Config.in
+		$< $(KCONF_FLAGS) --$(if $(confdefault),$(confdefault),old)config Config.in
 
 menuconfig: scripts/config/mconf prepare-tmpinfo FORCE
 	if [ \! -e .config -a -e $(HOME)/.openwrt/defconfig ]; then \
@@ -210,7 +213,7 @@ ifeq ($(SDK),1)
 
 %::
 	@+$(PREP_MK) $(NO_TRACE_MAKE) -r -s prereq
-	@./scripts/config/conf --defconfig=.config Config.in
+	@./scripts/config/conf $(KCONF_FLAGS) --defconfig=.config Config.in
 	@+$(ULIMIT_FIX) $(SUBMAKE) -r $@
 
 else
@@ -219,7 +222,7 @@ else
 	@+$(PREP_MK) $(NO_TRACE_MAKE) -r -s prereq
 	@( \
 		cp .config tmp/.config; \
-		./scripts/config/conf --defconfig=tmp/.config -w tmp/.config Config.in > /dev/null 2>&1; \
+		./scripts/config/conf $(KCONF_FLAGS) --defconfig=tmp/.config -w tmp/.config Config.in > /dev/null 2>&1; \
 		if ./scripts/kconfig.pl '>' .config tmp/.config | grep -q CONFIG; then \
 			printf "$(_R)WARNING: your configuration is out of sync. Please run make menuconfig, oldconfig or defconfig!$(_N)\n" >&2; \
 		fi \