Support external startup data in V8.

Support external startup data in V8.

[Retry of crrev.com/293993021, which caused problems with 'ninja all' in Chromium. First patch set if a clean apply
of crrev.com/293993021. Subsequent sets are the actual fix
for that issue.]

If the embedder chooses, the 'natives' (library sources) and the
precompiled startup blob can be written to files during the build
process and handed over to V8 at startup. The main purpose would be
to reduce the size of the compiled binary for space constrained
platforms.

The build-time option is off by default. Nothing should change if
it's not enabled.

BUG=
R=jochen@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21696

[jochen (gone - plz use gerrit), 2014-06-05 07:21:56]

lgtm

[vogelheim, 2014-06-05 13:06:38]

Committed patchset #2 manually as r21696 (presubmit successful).