cmd: extract obj's Biobuf code into new bio package

API could still be made more Go-ey.

Updates #15165.

Change-Id: I514ffceffa43c293ae5d7e5f1e9193fda0098865
Reviewed-on: https://go-review.googlesource.com/21644
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index ef8b516..cd9db38 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -6,6 +6,7 @@
 
 import (
 	"cmd/compile/internal/ssa"
+	"cmd/internal/bio"
 	"cmd/internal/obj"
 )
 
@@ -132,7 +133,7 @@
 
 var outfile string
 
-var bout *obj.Biobuf
+var bout *bio.Buf
 
 var nerrors int
 
@@ -287,7 +288,7 @@
 
 var writearchive int
 
-var bstdout obj.Biobuf
+var bstdout *bio.Buf
 
 var Nacl bool