cmd/compile/internal/gc: fix complex literal overflow

Change-Id: Ibb15282a2baeb58439b085d70b82797d8c71de36
Reviewed-on: https://go-review.googlesource.com/16502Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/lex.go

@@ -1535,7 +1535,7 @@ casei:
 	mpatoflt(&yylval.val.U.(*Mpcplx).Imag, str)
 	if yylval.val.U.(*Mpcplx).Imag.Val.IsInf() {
 		Yyerror("overflow in imaginary constant")
-		Mpmovecflt(&yylval.val.U.(*Mpcplx).Real, 0.0)
+		Mpmovecflt(&yylval.val.U.(*Mpcplx).Imag, 0.0)
 	}
 
 	if Debug['x'] != 0 {