GN: add target_arch build arg for android

GN: add target_arch build arg for android

This changes android to use the target_arch build arg for setting the
target architecture instead of cpu_arch.

Some benefits of this:
non-target toolchains have knowledge of the target architecture
(required for the relocation packer host executable)
allows us to have a default target_arch different from build_cpu_arch

BUG=359249, 344767
Committed: https://crrev.com/a7697bcfeed1dbbdafb419bc133e7d09774be485
Cr-Commit-Position: refs/heads/master@{#300136}

[cjhopman, 2014-10-16 18:38:21]

cjhopman@chromium.org changed reviewers:
+ brettw@chromium.org

[cjhopman, 2014-10-16 18:38:21]

brett, wdyt?

Also, it might make sense to change cpu_arch to not be automatically set at all
and then set it explicitly for all platforms in BUILDCONFIG.gn.

[brettw, 2014-10-16 19:19:07]

I'm OK making this for all platforms and setting the cpu_arch based on it (maybe
do a followup though). LGTM

https://codereview.chromium.org/634403004/diff/1/build/config/BUILDCONFIG.gn
File build/config/BUILDCONFIG.gn (right):

https://codereview.chromium.org/634403004/diff/1/build/config/BUILDCONFIG.gn#...
build/config/BUILDCONFIG.gn:76: # Architecture of the target device.
Can you add here something to the effect of "This will be equal to the cpu_arch
of the default toolchain. When checking the CPU architecture for source files
and build dependencies, you should almost always use cpu_arch instead. cpu_arch
is the architecture of the current toolchain, and using it allows cross-compiles
(compiling the same target for multiple toolchains in the same build) to be
supported.

[cjhopman, 2014-10-16 21:29:59]

https://codereview.chromium.org/634403004/diff/1/build/config/BUILDCONFIG.gn
File build/config/BUILDCONFIG.gn (right):

https://codereview.chromium.org/634403004/diff/1/build/config/BUILDCONFIG.gn#...
build/config/BUILDCONFIG.gn:76: # Architecture of the target device.
On 2014/10/16 19:19:07, brettw wrote:
> Can you add here something to the effect of "This will be equal to the
cpu_arch
> of the default toolchain. When checking the CPU architecture for source files
> and build dependencies, you should almost always use cpu_arch instead.
cpu_arch
> is the architecture of the current toolchain, and using it allows
cross-compiles
> (compiling the same target for multiple toolchains in the same build) to be
> supported.

Done.

https://codereview.chromium.org/634403004/diff/40001/build/config/BUILDCONFIG.gn
File build/config/BUILDCONFIG.gn (right):

https://codereview.chromium.org/634403004/diff/40001/build/config/BUILDCONFIG...
build/config/BUILDCONFIG.gn:77: # Architecture of the target device. For Android
builds, this will be equal to
This can't be guarded by (os == "android") because otherwise in a host toolchain
it isn't accessible (of course). The comment here reflects that it only affects
Android. If we are going to hook this up for other platforms, I guess we don't
really have to worry about it.

If we end up having a variable that we want to have accessible for target and
host toolchains for some configuration but not accessible at all for other
configurations, we would probably have to add something like target_os (just
like this target_arch).

[cjhopman, 2014-10-17 18:23:13]

The CQ bit was checked by cjhopman@chromium.org

[commit-bot: I haz the power, 2014-10-17 18:24:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/634403004/40001

[commit-bot: I haz the power, 2014-10-17 18:47:21]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2014-10-17 18:47:58]

Patchset 3 (id:??) landed as
https://crrev.com/a7697bcfeed1dbbdafb419bc133e7d09774be485
Cr-Commit-Position: refs/heads/master@{#300136}