Disable __NO_STRICT_ALIGNMENT on amd64/i386 for UBSan builds

This change allows to pick code paths in the kernel that are tuned for
alignment sensitive (and stricted in C meaning) code paths. In particular
the IPv6 code uses this heavily and skips whenever possible the process
of aligning of networking data.

With this modification all ATF tests are executed on amd64 without
triggering any UBSan reports in dmesg.

In theory __NO_STRICT_ALIGNMENT could be tuned for vax and m68k, however
these machines are still unsupported in LLVM sanitizers and syzkaller.

sys/netinet6/scope6.c:404:6, member access within misaligned address 0xfffffaea81276086 for type 'struct in6_addr' which requires 4 byte alignment
Reported-by: syzbot+a86f58d17685317b3df9@syzkaller.appspotmail.com

sys/net/rtsock_shared.c:629:41, member access within misaligned address 0xffffddb5db3ff04c for type 'struct rt_msghdr50' which requires 8 byte alignment
Reported-by: syzbot+0a3a022bc9d2b8880c16@syzkaller.appspotmail.com

sys/arch/amd64/include/types.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: types.h,v 1.61 2019/09/22 10:35:12 maxv Exp $	*/
+/*	$NetBSD: types.h,v 1.62 2019/09/23 23:06:26 kamil Exp $	*/
 
 /*-
  * Copyright (c) 1990 The Regents of the University of California.
@@ -74,8 +74,11 @@ typedef	unsigned char		__cpu_simple_lock_nv_t;
 #define	__SIMPLELOCK_LOCKED	1
 #define	__SIMPLELOCK_UNLOCKED	0
 
+#if !__has_feature(undefined_behavior_sanitizer) && \
+	!defined(__SANITIZE_UNDEFINED__)
 /* The amd64 does not have strict alignment requirements. */
 #define	__NO_STRICT_ALIGNMENT
+#endif
 
 #define	__HAVE_NEW_STYLE_BUS_H
 #define	__HAVE_CPU_COUNTER

sys/arch/i386/include/types.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: types.h,v 1.89 2019/04/06 03:06:25 thorpej Exp $	*/
+/*	$NetBSD: types.h,v 1.90 2019/09/23 23:06:26 kamil Exp $	*/
 
 /*-
  * Copyright (c) 1990 The Regents of the University of California.
@@ -99,8 +99,11 @@ typedef __register_t	register_t;
 #define	__SIMPLELOCK_LOCKED	1
 #define	__SIMPLELOCK_UNLOCKED	0
 
+#if !__has_feature(undefined_behavior_sanitizer) && \
+	!defined(__SANITIZE_UNDEFINED__)
 /* The x86 does not have strict alignment requirements. */
 #define	__NO_STRICT_ALIGNMENT
+#endif
 
 #define	__HAVE_NEW_STYLE_BUS_H
 #define	__HAVE_CPU_DATA_FIRST