boot/uboot: kconfig needs the toolchain

Starting with uboot 2021.10, with upstream commit 473fc279c89 (kconfig /
kbuild: Re-sync with Linux 4.20), the kconfig in uboot now needs the
compiler to detect its features.

Like was done for linux in 3fc990a7983 (linux: kconfig needs the
toolchain) and barebox in 1c1a629d814 (boot/barebox: kconfig needs the
toolchain), add the toolchain to the kconfig dependencies of uboot.

Reported-by: Davian on IRC
Reported-by: Xogium on IRC
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit c224e7e5c673b8a9c7eb7f3def1a2df2e959df4d)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/uboot/uboot.mk

@@ -500,7 +500,11 @@ UBOOT_DEPENDENCIES += \
 $(eval $(generic-package))
 else ifeq ($(BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG),y)
 UBOOT_MAKE_ENV = $(TARGET_MAKE_ENV)
+# Starting with 2021.10, the kconfig in uboot calls the cross-compiler
+# to check its capabilities. So we need the toolchain before we can
+# call the configurators.
 UBOOT_KCONFIG_DEPENDENCIES += \
+	toolchain \
 	$(BR2_MAKE_HOST_DEPENDENCY) \
 	$(BR2_BISON_HOST_DEPENDENCY) \
 	$(BR2_FLEX_HOST_DEPENDENCY)