Minimize no-change build time by only touching generated source files if they...

Minimize no-change build time by only touching generated source files if they
are changing

Ivan checked this in to v8's bleeding edge at r219.  (Thanks!)

[Mark Mentovai, 2008-09-09 01:00:02]

Ivan, the major change here is that we will only update the timestamp on
libraries.cc and libraries-empty.cc if the file contents are changing.  If
they're not changing, the timestamps will stay alone, so Xcode won't need to
rebuild them, relink libv8.a, and relink other things that depend on libv8.a in
the Chromium build.

I've also rolled in the two post-commit suggestions I had for this project file,
which are present in the version we're using for Chromium: I've added an "All"
target, and I've dropped the explicit /usr/local/bin installation directory
setting for v8_shell because that's already Xcode's default.

I'll need your help checking this in if you like it, since I don't have commit
access to the current v8 repository.

[iposva, 2008-09-09 02:57:00]

Mark,

This LGTM. I will take your change and submit it. The relink step for an
unchanged libraries.cc had started to annoy me as well. You just beat me to it.

-Ivan