[dev.cc] cmd/internal/obj: reconvert from liblink

Using rsc.io/c2go repo revision 60c9302.

- Export a few symbols needed by assemblers.
- Implement Getgoroot etc directly, and add Getgoversion.
- Removes dependency on Go 1.4 go/build.
- Change magic history name <no name> to <pop>

The <pop> change requires adjustment to the liblink serializer.

Change-Id: If5fb52ac9e91d50805263070b3fc5cc05d8b7632
Reviewed-on: https://go-review.googlesource.com/3141
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/internal/obj/util.go

@@ -7,7 +7,6 @@ package obj
 import (
 	"bufio"
 	"fmt"
-	"go/build"
 	"io"
 	"os"
 	"strconv"
@@ -76,16 +75,31 @@ func Bflush(b *Biobuf) error {
 	return b.w.Flush()
 }
 
+func envOr(key, value string) string {
+	if x := os.Getenv(key); x != "" {
+		return x
+	}
+	return value
+}
+
 func Getgoroot() string {
-	return build.Default.GOROOT
+	return envOr("GOROOT", defaultGOROOT)
 }
 
 func Getgoarch() string {
-	return build.Default.GOARCH
+	return envOr("GOARCH", defaultGOARCH)
 }
 
 func Getgoos() string {
-	return build.Default.GOOS
+	return envOr("GOOS", defaultGOOS)
+}
+
+func Getgoarm() string {
+	return envOr("GOARM", defaultGOARM)
+}
+
+func Getgoversion() string {
+	return version
 }
 
 func Atoi(s string) int {
@@ -93,14 +107,6 @@ func Atoi(s string) int {
 	return i
 }
 
-func Getgoarm() string {
-	env := os.Getenv("GOARM")
-	if env != "" {
-		return env
-	}
-	return "5"
-}
-
 func (p *Prog) Line() string {
 	return linklinefmt(p.Ctxt, int(p.Lineno), false, false)
 }