5c: make alignment rules match 5g, just like 6c matches 6g

I should have done this a year ago in:

        changeset:   5137:686b18098944
        user:        Russ Cox <rsc@golang.org>
        date:        Thu Mar 25 14:05:54 2010 -0700
        files:       src/cmd/8c/swt.c
        description:
        make alignment rules match 8g, just like 6c matches 6g.

        R=ken2
        CC=golang-dev
        https://golang.org/cl/760042

R=ken2
CC=golang-dev
https://golang.org/cl/4437054

src/cmd/5c/swt.c

@@ -665,7 +665,9 @@ align(int32 i, Type *t, int op, int32 *maxalign)
 
 	case Aarg2:	/* width of a parameter */
 		o += t->width;
-		w = SZ_LONG;
+		w = t->width;
+		if(w > SZ_LONG)
+			w = SZ_LONG;
 		break;
 
 	case Aaut3:	/* total align of automatic */