Remove -Wa,--noexecstack flag on Android.

Remove -Wa,--noexecstack flag on Android.

This flag causes unused argument errors when using LTO (or Clang's integrated
assembler), and is not needed to disable executable stacks, as we are already
passing -Wl,-z,noexecstack at link time, which is how executable stacks are
already getting disabled on other platforms.

BUG=407544
R=thakis@chromium.org
TEST=Built libchromeshell.so with default GYP_DEFINES with and without this change, verified that binaries are equivalent

Committed: https://crrev.com/8c865340749de6de14d68b64d69af6942e445f69
Cr-Commit-Position: refs/heads/master@{#325375}

[Nico, 2015-04-15 16:40:47]

Does assembler output always go through the linker? Or is there a way to
effectively run `nasm -f bin input.asm` through the cc driver?

[pcc1, 2015-04-16 00:46:59]

On 2015/04/15 16:40:47, Nico wrote:
> Does assembler output always go through the linker?

I couldn't spot any cases where it doesn't go through the linker. I also
verified that the libchromeshell DSO is identical after this change. I've
updated the CL description with that result.

[Nico, 2015-04-16 00:54:46]

The CQ bit was checked by thakis@chromium.org

[Nico, 2015-04-16 00:54:46]

lgtm

[commit-bot: I haz the power, 2015-04-16 00:55:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1091463002/1

[commit-bot: I haz the power, 2015-04-16 02:08:28]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 02:09:34]

Patchset 1 (id:??) landed as
https://crrev.com/8c865340749de6de14d68b64d69af6942e445f69
Cr-Commit-Position: refs/heads/master@{#325375}