Add support for building the ARM simulator to Xcode

[ipo...@chromium.org]

Reviewers: Mark Mentovai,

Description:
Add support for building the ARM simulator version of V8 to the Xcode
project.
The next step for the Xcode project is to update the file list and then
to mirror the xcconfigs.

Please review this at http://codereview.chromium.org/1948

Affected files:
M tools/v8.xcodeproj/project.pbxproj