Set default cross compiler for ARM/linux builds.

Set default cross compiler for ARM/linux builds.

Currently this relies on the user setting these variables
outside of gyp and outside of source control.  Once this
lands the buildbot configs can be simplified to remove
these variables.

Even though we are trying to switch to clang by default
in the short term, this is still useful for building
with gcc on trusty (which has gcc 4.8), and allows us to
simplify the bot configs.

BUG=395832
R=thakis@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=286219

[Mark Seaborn, 2014-07-28 15:55:20]

Can you set BUG=395832?

The change looks OK to me, but common.gypi is quite hairy, so I'd like Nico or
Brad to take a look because they probably understand the subtleties better than
me.

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:3390: # Some sensible defaults for ARM cross compiling on
linux.  These can be overridden
Line is >80 chars

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:3393: ['CC', '<!(which arm-linux-gnueabihf-gcc)'],
The bot configs also set AR, AS and RANLIB (see
https://src.chromium.org/viewvc/chrome/trunk/tools/build/scripts/slave/recipe...).
 Are any of those necessary?

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:5590: ['CC', '<(sysroot)/../bin/mipsel-linux-gnu-gcc'],
Should your code go after these blocks, which are similar?

[Nico, 2014-07-28 16:01:41]

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:5590: ['CC', '<(sysroot)/../bin/mipsel-linux-gnu-gcc'],
On 2014/07/28 15:55:20, Mark Seaborn wrote:
> Should your code go after these blocks, which are similar?

+1, if that works that'd be better.

[Sam Clegg, 2014-07-29 00:28:11]

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:3390: # Some sensible defaults for ARM cross compiling on
linux.  These can be overridden
On 2014/07/28 15:55:20, Mark Seaborn wrote:
> Line is >80 chars

There are other occurrences of conditions in this file that overflow the 80 char
line so I assumed that was ok (line 110, line 211 for example).

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:3393: ['CC', '<!(which arm-linux-gnueabihf-gcc)'],
On 2014/07/28 15:55:20, Mark Seaborn wrote:
> The bot configs also set AR, AS and RANLIB (see
>
https://src.chromium.org/viewvc/chrome/trunk/tools/build/scripts/slave/recipe...).
>  Are any of those necessary?

Apparently not.  Its hard to be 100% since there are C++11 issues that currently
make building with arm/gcc on precise impossible, but I can build many targets.

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:5590: ['CC', '<(sysroot)/../bin/mipsel-linux-gnu-gcc'],
On 2014/07/28 15:55:20, Mark Seaborn wrote:
> Should your code go after these blocks, which are similar?

Done.

https://codereview.chromium.org/414343003/diff/20001/build/common.gypi#newcod...
build/common.gypi:5590: ['CC', '<(sysroot)/../bin/mipsel-linux-gnu-gcc'],
On 2014/07/28 16:01:40, Nico (away) wrote:
> On 2014/07/28 15:55:20, Mark Seaborn wrote:
> > Should your code go after these blocks, which are similar?
> 
> +1, if that works that'd be better.

Done.

[Nico, 2014-07-29 00:30:29]

lgtm

[Sam Clegg, 2014-07-29 16:52:52]

Committed patchset #3 manually as r286219 (presubmit successful).