cmd/compile: give TLS relocations a name when dumping assembly

Before:

	...
	0x00d0 ff ff ff e8 00 00 00 00 e9 23 ff ff ff cc cc cc  .........#......
	rel 5+4 t=14 +0
	rel 82+4 t=13 runtime.writeBarrier+0
	...

After:

	...
	0x00d0 ff ff ff e8 00 00 00 00 e9 23 ff ff ff cc cc cc  .........#......
	rel 5+4 t=14 TLS+0
	rel 82+4 t=13 runtime.writeBarrier+0
	...

Change-Id: Ibdaf694581b5fd5fb87fa8ce6a792f3eb4493622
Reviewed-on: https://go-review.googlesource.com/21545Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/obj/objfile.go

@@ -553,6 +553,8 @@ func (w *objWriter) writeSymDebug(s *LSym) {
 		name := ""
 		if r.Sym != nil {
 			name = r.Sym.Name
+		} else if r.Type == R_TLS_LE {
+			name = "TLS"
 		}
 		if ctxt.Arch.Thechar == '5' || ctxt.Arch.Thechar == '9' {
 			fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s+%x\n", int(r.Off), r.Siz, r.Type, name, uint64(int64(r.Add)))