package/linux: don't leak host timezone into linux version string

Signed-off-by: Nuno Gonçalves <nunog@fr24.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit a848418db4f956486a17dedc08f09803b26c84a1)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -162,7 +162,7 @@ LINUX_MAKE_ENV += \
 	KBUILD_BUILD_VERSION=1 \
 	KBUILD_BUILD_USER=buildroot \
 	KBUILD_BUILD_HOST=buildroot \
-	KBUILD_BUILD_TIMESTAMP="$(shell LC_ALL=C date -d @$(SOURCE_DATE_EPOCH))"
+	KBUILD_BUILD_TIMESTAMP="$(shell LC_ALL=C TZ='UTC' date -d @$(SOURCE_DATE_EPOCH))"
 endif
 
 # gcc-8 started warning about function aliases that have a