cmd/compile: remove dead flags

For some time now, the -d flag has been used to control various named
debug options, rather than setting Debug['d']. Consequently, that
means dflag() always returns false, which means the -y flag is also
useless.

Similarly, Debug['L'] is never used anywhere, so the -L flag can be
dropped too.

Change-Id: I4bb12454e462410115ec4f5565facf76c5c2f255
Reviewed-on: https://go-review.googlesource.com/22121Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -13,19 +13,6 @@ import (
 
 // Declaration stack & operations
 
-func dflag() bool {
-	if Debug['d'] == 0 {
-		return false
-	}
-	if Debug['y'] != 0 {
-		return true
-	}
-	if incannedimport != 0 {
-		return false
-	}
-	return true
-}
-
 var externdcl []*Node
 
 var blockgen int32 // max block number
@@ -67,9 +54,6 @@ func push() *Sym {
 func pushdcl(s *Sym) *Sym {
 	d := push()
 	dcopy(d, s)
-	if dflag() {
-		fmt.Printf("\t%v push %v %p\n", linestr(lineno), s, s.Def)
-	}
 	return d
 }
 
@@ -82,9 +66,6 @@ func popdcl() {
 		lno := s.Lastlineno
 		dcopy(s, d)
 		d.Lastlineno = lno
-		if dflag() {
-			fmt.Printf("\t%v pop %v %p\n", linestr(lineno), s, s.Def)
-		}
 	}
 
 	if d == nil {
@@ -194,9 +175,6 @@ func declare(n *Node, ctxt Class) {
 	gen := 0
 	if ctxt == PEXTERN {
 		externdcl = append(externdcl, n)
-		if dflag() {
-			fmt.Printf("\t%v global decl %v %p\n", linestr(lineno), s, n)
-		}
 	} else {
 		if Curfn == nil && ctxt == PAUTO {
 			Fatalf("automatic outside function")

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

@@ -153,7 +153,6 @@ func Main() {
 	obj.Flagcount("E", "debug symbol export", &Debug['E'])
 	obj.Flagfn1("I", "add `directory` to import search path", addidir)
 	obj.Flagcount("K", "debug missing line numbers", &Debug['K'])
-	obj.Flagcount("L", "use full (long) path in error messages", &Debug['L'])
 	obj.Flagcount("M", "debug move generation", &Debug['M'])
 	obj.Flagcount("N", "disable optimizations", &Debug['N'])
 	obj.Flagcount("P", "debug peephole optimizer", &Debug['P'])
@@ -191,7 +190,6 @@ func Main() {
 	obj.Flagcount("w", "debug type checking", &Debug['w'])
 	flag.BoolVar(&use_writebarrier, "wb", true, "enable write barrier")
 	obj.Flagcount("x", "debug lexer", &Debug['x'])
-	obj.Flagcount("y", "debug declarations in canned imports (with -d)", &Debug['y'])
 	var flag_shared bool
 	var flag_dynlink bool
 	if supportsDynlink(Thearch.LinkArch.Arch) {