[NaCl SDK] Allow dsc files to omit TOOLS setting

[NaCl SDK] Allow dsc files to omit TOOLS setting

The default is to support all toolchains. Do this
for several core libraries. This mostly affects
mac for which these libraries were previously not
being built.

This change allows for the addition of nacl-clang
or other toolchain without needing to change all
the core dsc files.

BUG=454962
Committed: https://crrev.com/4b386c1c9ea6286197c62a30d3aa800e7400a0c9
Cr-Commit-Position: refs/heads/master@{#314623}

[Sam Clegg, 2015-02-03 22:25:33]

sbc@chromium.org changed reviewers:
+ bradnelson@chromium.org

[bradn, 2015-02-04 10:41:37]

bradnelson@google.com changed reviewers:
+ bradnelson@google.com

[bradn, 2015-02-04 10:41:38]

lgtm

[Sam Clegg, 2015-02-04 18:28:36]

New patchsets have been uploaded after l-g-t-m from bradnelson@google.com

[Sam Clegg, 2015-02-04 19:30:20]

The CQ bit was checked by sbc@chromium.org

[commit-bot: I haz the power, 2015-02-04 19:31:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/886583004/80001

[Sam Clegg, 2015-02-04 19:33:26]

The CQ bit was unchecked by sbc@chromium.org

[Sam Clegg, 2015-02-04 20:34:13]

The CQ bit was checked by sbc@chromium.org

[commit-bot: I haz the power, 2015-02-04 20:35:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/886583004/80001

[commit-bot: I haz the power, 2015-02-04 20:36:41]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2015-02-04 20:37:43]

Patchset 5 (id:??) landed as
https://crrev.com/4b386c1c9ea6286197c62a30d3aa800e7400a0c9
Cr-Commit-Position: refs/heads/master@{#314623}