target/alpha: Implement alpha_cpu_record_sigbus

Record trap_arg{0,1,2} for the linux-user signal frame.

Raise SIGBUS directly from cpu_loop_exit_sigbus, which means
we can remove the code for EXCP_UNALIGN in cpu_loop.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/alpha/cpu_loop.c

@@ -54,13 +54,6 @@ void cpu_loop(CPUAlphaState *env)
             fprintf(stderr, "External interrupt. Exit\n");
             exit(EXIT_FAILURE);
             break;
-        case EXCP_UNALIGN:
-            info.si_signo = TARGET_SIGBUS;
-            info.si_errno = 0;
-            info.si_code = TARGET_BUS_ADRALN;
-            info._sifields._sigfault._addr = env->trap_arg0;
-            queue_signal(env, info.si_signo, QEMU_SI_FAULT, &info);
-            break;
         case EXCP_OPCDEC:
         do_sigill:
             info.si_signo = TARGET_SIGILL;