code review 5530050: libmach: cross compiling support

libmach: cross compiling support
        We already use GOHOSTOS to represent the host OS that the toolchain
        will be run on, so no need to resort to uname(1) to get that (and
        use uname(1) will make cross-compiling for another host impossible).

[minux1, 2012-01-09 08:43:09]

Hello rsc@golang.org, golang-dev@googlegroups.com (cc:
golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[minux1, 2012-01-20 12:12:10]

Gentle ping.

IMHO, this CL make the libmach/Makefile's intent more clear and 
the handling of $GOHOSTARCH more consistent.
(Why only windows is a special case? Why disregard all the other 
values for $GOHOSTARCH?)

This CL certainly won't break anything, but it makes cross compiling 
Go distribution for another architecture possible (this capability 
is useful for low-powered architectures like ARM).

Also, I could provide an wiki entry explaining how to do this.
(Also consider we don't have a Plan 9 builder, this could help if
we could make a Plan 9 cross compiler available [at least build
won't break on Plan 9].)

[rsc, 2012-01-20 18:30:28]

LGTM

[rsc, 2012-01-20 18:34:32]

*** Submitted as http://code.google.com/p/go/source/detail?r=8fc7d691465c ***

libmach: cross compiling support
        We already use GOHOSTOS to represent the host OS that the toolchain
        will be run on, so no need to resort to uname(1) to get that (and
        use uname(1) will make cross-compiling for another host impossible).

R=rsc, golang-dev
CC=golang-dev
http://codereview.appspot.com/5530050

Committer: Russ Cox <rsc@golang.org>