Default-enable external startup data for Linux for stand-alone builds.

Default-enable external startup data for Linux for stand-alone builds.

Notes:
- Other platforms to follow later.
- This follows Chromium practice, that mostly uses this feature these days.
- The statically linked-in startup data will stay. So whoever prefers
  the old way just needs to set the flag differently.

Reland crrev.com/959693002, once crrev.com/960883003 is in.

R=machenbach@chromium.org
BUG=

Committed: https://crrev.com/a0bdb103b676b4c7fa6b9f2e7149e716549c05d1
Cr-Commit-Position: refs/heads/master@{#26980}

[Michael Achenbach, 2015-02-26 17:08:58]

lgtm

[vogelheim, 2015-03-03 17:44:49]

Patchset #2 (id:20001) has been deleted

[vogelheim, 2015-03-03 17:44:55]

Patchset #2 (id:40001) has been deleted

[vogelheim, 2015-03-04 12:19:34]

The CQ bit was checked by vogelheim@chromium.org

[commit-bot: I haz the power, 2015-03-04 12:20:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/956373002/1

[commit-bot: I haz the power, 2015-03-04 12:21:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-04 12:22:08]

Patchset 1 (id:??) landed as
https://crrev.com/a0bdb103b676b4c7fa6b9f2e7149e716549c05d1
Cr-Commit-Position: refs/heads/master@{#26980}

[vogelheim, 2015-03-04 13:52:07]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/981463005/ by vogelheim@chromium.org.

The reason for reverting is: The CL caused two issues:
- a weird build issue on V8 mips builder
- d8 cannot be invoked via PATH, since then it doesn't find its external
snapshot.

The 2nd issue might even be WAI, but this needs more consideration..

[vogelheim, 2015-03-26 15:34:16]

Patchset #2 (id:60001) has been deleted