document the assemblers.

add details about -d and -e flags in the loaders.

R=rsc
CC=go-dev
http://go/go-review/1018031

src/cmd/5a/doc.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+
+5a is a version of the Plan 9 assembler documented at
+
+	http://plan9.bell-labs.com/magic/man2html/1/2a
+
+Its target architecture is the ARM, referred to by these tools as arm.
+
+*/
+package documentation

src/cmd/6a/doc.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+
+6a is a version of the Plan 9 assembler documented at
+
+	http://plan9.bell-labs.com/magic/man2html/1/2a
+
+Its target architecture is the x86-64, referred to by these tools as amd64.
+
+*/
+package documentation

src/cmd/6l/doc.go

@@ -19,6 +19,13 @@ Original options are listed in the link above.
 
 Options new in this version:
 
+-d
+	Elide the dynamic linking header.  With this option, the binary
+	is statically linked and does not refer to dynld.  Without this option
+	(the default), the binary's contents are identical but it is loaded with dynld.
+-e
+	Emit an extra ELF-compatible symbol table useful with tools such as
+	nm, gdb, and oprofile. This option makes the binary file considerably larger.
 -H6
 	Write Apple Mach-O binaries (default when $GOOS is darwin)
 -H7

src/cmd/8a/doc.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+
+8a is a version of the Plan 9 assembler documented at
+
+	http://plan9.bell-labs.com/magic/man2html/1/2a
+
+Its target architecture is the x86, referred to by these tools for historical reasons as 386.
+
+*/
+package documentation

src/cmd/8l/doc.go

@@ -19,6 +19,10 @@ Original options are listed in the link above.
 
 Options new in this version:
 
+-d
+	Elide the dynamic linking header.  With this option, the binary
+	is statically linked and does not refer to dynld.  Without this option
+	(the default), the binary's contents are identical but it is loaded with dynld.
 -H6
 	Write Apple Mach-O binaries (default when $GOOS is darwin)
 -H7