Add support for the GYP_CROSSCOMPILE env var to MB.

Add support for the GYP_CROSSCOMPILE env var to MB.

This is needed to support building the "Linux ARM" configurations w/ MB,
which are cross-compiles but the target os is linux, not android or iOS.
Theoretically it might be needed for a real CrOS compile as well. You
can now specify that a cross-compile is needed with the 'crosscompile'
mixin.

We don't normally need this flag for android and ios builds, because
gyp_chromium sets it for us when target_os={android,ios}.

R=thakis@chromium.org
BUG=481692
Committed: https://crrev.com/edc49c383f30998c2a06fee632bac6cbf71817c2
Cr-Commit-Position: refs/heads/master@{#343327}

[Nico, 2015-08-14 00:14:30]

lgtm, two optional suggestions below.

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb.py
File tools/mb/mb.py (right):

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb.py#newcode438
tools/mb/mb.py:438: env['GYP_CROSSCOMPILE'] = '1'
Hm, this copy-env-and-set pattern has caused me trouble on Windows in the past
(https://codereview.chromium.org/1187933002). Maybe only do the copy if needed,
like I'm doing in that CL.

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb_config.pyl
File tools/mb/mb_config.pyl (right):

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb_config.pyl#newc...
tools/mb/mb_config.pyl:134: 'crosscompile': {
Maybe add a comment that it's usually not necessary to add this.

[Dirk Pranke, 2015-08-14 00:19:17]

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb.py
File tools/mb/mb.py (right):

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb.py#newcode438
tools/mb/mb.py:438: env['GYP_CROSSCOMPILE'] = '1'
On 2015/08/14 00:14:30, Nico (hiding) wrote:
> Hm, this copy-env-and-set pattern has caused me trouble on Windows in the past
> (https://codereview.chromium.org/1187933002). Maybe only do the copy if
needed,
> like I'm doing in that CL.

I'm not sure why that would make a difference, but okay :).

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb_config.pyl
File tools/mb/mb_config.pyl (right):

https://codereview.chromium.org/1294663002/diff/1/tools/mb/mb_config.pyl#newc...
tools/mb/mb_config.pyl:134: 'crosscompile': {
On 2015/08/14 00:14:30, Nico (hiding) wrote:
> Maybe add a comment that it's usually not necessary to add this.

Will do.

[Dirk Pranke, 2015-08-14 00:19:22]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-08-14 00:19:22]

The patchset sent to the CQ was uploaded after l-g-t-m from thakis@chromium.org
Link to the patchset: https://codereview.chromium.org/1294663002/#ps20001
(title: "update w/ review feedback")

[commit-bot: I haz the power, 2015-08-14 00:19:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1294663002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1294663002/20001

[commit-bot: I haz the power, 2015-08-14 02:33:04]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-08-14 02:33:41]

Patchset 2 (id:??) landed as
https://crrev.com/edc49c383f30998c2a06fee632bac6cbf71817c2
Cr-Commit-Position: refs/heads/master@{#343327}