linux-user: fix x86_64 safe_syscall

Do what the comment says, test for signal_pending non-zero,
rather than the current code which tests for bit 0 non-zero.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

linux-user/host/x86_64/safe-syscall.inc.S

@@ -67,8 +67,8 @@ safe_syscall_base:
          */
 safe_syscall_start:
         /* if signal_pending is non-zero, don't do the call */
-        testl   $1, (%rbp)
-        jnz     return_ERESTARTSYS
+        cmpl	$0, (%rbp)
+        jnz     1f
         syscall
 safe_syscall_end:
         /* code path for having successfully executed the syscall */
@@ -78,7 +78,7 @@ safe_syscall_end:
         .cfi_restore rbp
         ret
 
-return_ERESTARTSYS:
+1:
         /* code path when we didn't execute the syscall */
         .cfi_restore_state
         mov     $-TARGET_ERESTARTSYS, %rax