x86/vdso: Ensure all kernel code is seen by objtool

extable.c is kernel code and not part of the VDSO
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111143.512144110@infradead.org

arch/x86/entry/vdso/Makefile

@@ -38,6 +38,7 @@ KASAN_SANITIZE_vma.o		:= y
 UBSAN_SANITIZE_vma.o			:= y
 KCSAN_SANITIZE_vma.o			:= y
 OBJECT_FILES_NON_STANDARD_vma.o		:= n
+OBJECT_FILES_NON_STANDARD_extable.o	:= n
 
 # vDSO images to build
 vdso_img-$(VDSO64-y)		+= 64