cmd/link: more idiomatic object reader

name       old secs    new secs    delta
LinkCmdGo   0.52 ± 3%   0.52 ± 7%    ~     (p=0.325 n=93+100)

name       old MaxRSS  new MaxRSS  delta
LinkCmdGo   120k ± 1%   118k ± 4%  -1.10%   (p=0.000 n=87+96)

Change-Id: I967660b8dc6036d28eeea1b6b30f400fadd57b05
Reviewed-on: https://go-review.googlesource.com/21372
Run-TryBot: Shahar Kohanim <skohanim@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -1347,7 +1347,7 @@ func ldobj(f *obj.Biobuf, pkg string, length int64, pn string, file string, when
 	ldpkg(f, pkg, import1-import0-2, pn, whence) // -2 for !\n
 	obj.Bseek(f, import1, 0)
 
-	ldobjfile(Ctxt, f, pkg, eof-obj.Boffset(f), pn)
+	LoadObjFile(Ctxt, f, pkg, eof-obj.Boffset(f), pn)
 	return nil
 }
 

src/cmd/link/internal/ld/link.go

@@ -189,7 +189,6 @@ type Link struct {
 	Filesyms   *LSym
 	Moduledata *LSym
 	LSymBatch  []LSym
-	CurRefs    []*LSym // List of symbol references for the file being read.
 }
 
 // The smallest possible offset from the hardware stack pointer to a local