kbuild: Update Makefile.extrawarn to 5.1

Since we are updating our kbuild system to 5.1, add the relevant
clang changes from upstream

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index f687515..7df6226 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -67,5 +67,14 @@
 endif
 
 KBUILD_CFLAGS += $(warning)
+else
 
+ifdef CONFIG_CC_IS_CLANG
+KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
+KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
+KBUILD_CFLAGS += $(call cc-disable-warning, format)
+KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
+KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
+KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
+endif
 endif