linux-user: Exit not abort in die_with_backtrace

This line is supposed to be unreachable, but if we're going to
have it at all, SIGABRT via abort() is subject to the same signal
peril that created this function in the first place.

We can _exit immediately without peril.

Acked-by: Helge Deller <deller@gmx.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/signal.c

@@ -713,7 +713,7 @@ void die_with_signal(int host_sig)
     sigsuspend(&act.sa_mask);
 
     /* unreachable */
-    abort();
+    _exit(EXIT_FAILURE);
 }
 
 static G_NORETURN