Use host instead of current OS for NaCl toolchain location

Use host instead of current OS for NaCl toolchain location

We should be using the host OS for determining the toolchain location
as this is the OS toolchain is going to be running on.

BUG=462791
Committed: https://crrev.com/f68cf5be7c8cd51e51a5c02777053518b2e529e9
Cr-Commit-Position: refs/heads/master@{#350734}

[Petr Hosek, 2015-09-25 00:21:32]

phosek@chromium.org changed reviewers:
+ dpranke@chromium.org

[Dirk Pranke, 2015-09-25 00:21:58]

lgtm

[Petr Hosek, 2015-09-25 00:24:03]

The CQ bit was checked by phosek@chromium.org

[commit-bot: I haz the power, 2015-09-25 00:24:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1366153002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1366153002/1

[commit-bot: I haz the power, 2015-09-25 01:19:41]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-25 01:20:28]

Patchset 1 (id:??) landed as
https://crrev.com/f68cf5be7c8cd51e51a5c02777053518b2e529e9
Cr-Commit-Position: refs/heads/master@{#350734}