kcsan, ubsan: Make KCSAN+UBSAN work together

Context:
http://lkml.kernel.org/r/fb7e25d8-aba4-3dcf-7761-cb7ecb3ebb71@infradead.orgReported-by: NRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: NMarco Elver <elver@google.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>

kernel/kcsan/Makefile

 # SPDX-License-Identifier: GPL-2.0
 KCSAN_SANITIZE := n
 KCOV_INSTRUMENT := n
+UBSAN_SANITIZE := n
 
 CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
 

lib/Makefile

@@ -279,6 +279,7 @@ obj-$(CONFIG_UBSAN) += ubsan.o
 
 UBSAN_SANITIZE_ubsan.o := n
 KASAN_SANITIZE_ubsan.o := n
+KCSAN_SANITIZE_ubsan.o := n
 CFLAGS_ubsan.o := $(call cc-option, -fno-stack-protector) $(DISABLE_STACKLEAK_PLUGIN)
 
 obj-$(CONFIG_SBITMAP) += sbitmap.o