linux-user: Fix s390x safe-syscall for z900

The LT instruction was added in the extended immediate facility
introduced with the z9-109 processor.

Cc: Riku Voipio <riku.voipio@iki.fi>
Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Fixes: c9bc3437a9
Suggested-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/host/s390x/safe-syscall.inc.S

@@ -72,7 +72,7 @@ safe_syscall_base:
 	 */
 safe_syscall_start:
 	/* if signal_pending is non-zero, don't do the call */
-	lt	%r0,0(%r8)
+	icm	%r0,15,0(%r8)
 	jne	2f
 	svc	0
 safe_syscall_end: