[dev.link] cmd: support large function alignment

This ports CL 226997 to the dev.link branch.
- The assembler part and old object file writing are unchanged.
- Changes to cmd/link are applied to cmd/oldlink.
- Add alignment field to new object files for the new linker.

Change-Id: Id00f323ae5bdd86b2709a702ee28bcaa9ba962f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/227025
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/internal/obj/link.go

@@ -398,6 +398,7 @@ type LSym struct {
 type FuncInfo struct {
 	Args     int32
 	Locals   int32
+	Align    int32
 	Text     *Prog
 	Autot    map[*LSym]struct{}
 	Pcln     Pcln