cmd: remove bio.BufReader and bio.BufWriter

bio.BufReader was never used.

bio.BufWriter was used to wrap an existing io.Writer, but the
bio.Writer returned would not be seekable, so replace all occurences
with bufio.Reader instead.

Change-Id: I9c6779e35c63178aa4e104c17bb5bb8b52de0359
Reviewed-on: https://go-review.googlesource.com/21722
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Dave Cheney <dave@cheney.net>
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 ec7e219..d9b28ff 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -5,6 +5,7 @@
 package gc
 
 import (
+	"bufio"
 	"cmd/compile/internal/ssa"
 	"cmd/internal/bio"
 	"cmd/internal/obj"
@@ -288,7 +289,7 @@
 
 var writearchive int
 
-var bstdout *bio.Writer
+var bstdout *bufio.Writer
 
 var Nacl bool