cmd/internal/obj: remove Link.Debugdivmod

It is only used once and never written to.
Switch to a local constant instead.

Change-Id: Icdd84e47b81f0de44ad9ed56ab5f4f91df22e6b6
Reviewed-on: https://go-review.googlesource.com/40405
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/internal/obj/arm/obj5.go

@@ -537,7 +537,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			if cursym.Text.From3.Offset&obj.NOSPLIT != 0 {
 				ctxt.Diag("cannot divide in NOSPLIT function")
 			}
-			if ctxt.Debugdivmod {
+			const debugdivmod = false
+			if debugdivmod {
 				break
 			}
 			if p.From.Type != obj.TYPE_REG {

src/cmd/internal/obj/link.go

@@ -715,7 +715,6 @@ type Link struct {
 	Arch          *LinkArch
 	Debugasm      bool
 	Debugvlog     bool
-	Debugdivmod   bool
 	Debugpcln     string
 	Flag_shared   bool
 	Flag_dynlink  bool