linux: kconfig may need host-{flex, bison} to build the configurators

Rely on the system provided ones if avalable, and only resort to use our
owns if the sytem does not provide them.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Jan Kundrát <jan.kundrat@cesnet.cz>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

linux/linux.mk

@@ -64,12 +64,18 @@ LINUX_PATCH = $(filter ftp://% http://% https://%,$(LINUX_PATCHES))
 LINUX_INSTALL_IMAGES = YES
 LINUX_DEPENDENCIES = host-kmod
 
-# Starting with 4.16, the generated kconfig paser code is no longer
-# shipped with the kernel sources, so we need flex and bison.
 # Starting with 4.17, the generated dtc parser code is no longer
-# shipped with the kernel sources, so we need flex and bison.
+# shipped with the kernel sources, so we need flex and bison. For
+# reproducibility, we use our owns rather than the host ones.
 LINUX_DEPENDENCIES += host-bison host-flex
 
+# Starting with 4.16, the generated kconfig paser code is no longer
+# shipped with the kernel sources, so we need flex and bison, but
+# only if the host does not have them.
+LINUX_KCONFIG_DEPENDENCIES = \
+	$(BR2_BISON_HOST_DEPENDENCY) \
+	$(BR2_FLEX_HOST_DEPENDENCY)
+
 # host tools needed for kernel compression
 ifeq ($(BR2_LINUX_KERNEL_LZ4),y)
 LINUX_DEPENDENCIES += host-lz4