[Buildroot] [git commit branch/2022.02.x] linux/linux.mk: ensure custom kernel version is set

[Peter Korsgaard]

commit: https://git.buildroot.net/buildroot/commit/?id=2abfc4ac716578d1584d670988ba66174762b1fe
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/2022.02.x

Validate that BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE is set when
required.

Fixes:
http://autobuild.buildroot.net/results/117/117c08e414776202446a9fdb96d084aa3c16af48

Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
(cherry picked from commit 84b1eacc328baad3ceb63505ac588022620a05f6)
Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
---
 linux/linux.mk | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/linux/linux.mk b/linux/linux.mk
index 102b7a15d4..7ff7b05042 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -566,6 +566,12 @@ endif
 
 ifeq ($(BR_BUILDING),y)
 
+ifeq ($(BR2_LINUX_KERNEL_CUSTOM_VERSION),y)
+ifeq ($(LINUX_VERSION),)
+$(error No custom kernel version set. Check your BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE setting)
+endif
+endif
+
 ifeq ($(BR2_LINUX_KERNEL_USE_DEFCONFIG),y)
 # We must use the user-supplied kconfig value, because
 # LINUX_KCONFIG_DEFCONFIG will at least contain the