s390/boot: turn off KMSAN

All other sanitizers are disabled for boot as well.  While at it, add a
comment explaining why we need this.

Link: https://lkml.kernel.org/r/20240621113706.315500-23-iii@linux.ibm.comSigned-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <kasan-dev@googlegroups.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/s390/boot/Makefile

@@ -3,11 +3,13 @@
 # Makefile for the linux s390-specific parts of the memory manager.
 #
 
+# Tooling runtimes are unavailable and cannot be linked for early boot code
 KCOV_INSTRUMENT := n
 GCOV_PROFILE := n
 UBSAN_SANITIZE := n
 KASAN_SANITIZE := n
 KCSAN_SANITIZE := n
+KMSAN_SANITIZE := n
 
 KBUILD_AFLAGS := $(KBUILD_AFLAGS_DECOMPRESSOR)
 KBUILD_CFLAGS := $(KBUILD_CFLAGS_DECOMPRESSOR)