target-alpha: Use noreturn marker in helper.h.

Signed-off-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

target-alpha/helper.h

 #include "def-helper.h"
 
-DEF_HELPER_3(excp, void, env, int, int)
+DEF_HELPER_3(excp, noreturn, env, int, int)
 DEF_HELPER_FLAGS_1(load_pcc, TCG_CALL_CONST | TCG_CALL_PURE, i64, env)
 
 DEF_HELPER_3(addqv, i64, env, i64, i64)