LSK: record a known bug on x86 with KASAN

A KASAN bug introduced by KASAN backporting to ARM

Signed-off-by: Alex Shi <alex.shi@linaro.org>
diff --git a/known-bugs b/known-bugs
index e4f6dbb..9b87584 100644
--- a/known-bugs
+++ b/known-bugs
@@ -1,4 +1,7 @@
 1, Kernel build error when ARCH=arm with multi_v7_defconfig+CONFIG_SMP=n 
 	arch/arm/kernel/psci.c:287:115: error: redefinition of 'psci_init'
   This bug start from commit dbcfee724255ae1 ARM: 8457/1: psci-smp is built only for SMP
-
+2, Kernel build error when ARCH=x86 with allmodconfig+CONFIG_OF=n or defconfig+CONFIG_KASAN=y
+	include/linux/kasan.h:21:14: error: conflicting types for 'kasan_zero_pud'
+	include/linux/kasan.h:20:14: error: conflicting types for 'kasan_zero_pmd'
+  This bug is due to KASAN feature backporting