This patch speeds up the startup time and reduce the startup memory
footprint by using V8 code cache when comiling builtin modules.

The current approach is demonstrated in the `with-code-cache`
Makefile target (no corresponding Windows target at the moment).

1. Build the binary normally (`src/node_code_cache_stub.cc` is used),
  by now `internalBinding('code_cache')` is an empty object
2. Run `tools/generate_code_cache.js` with the binary, which generates
  the code caches by reading source code of builtin modules off source
  code exposed by `require('internal/bootstrap/cache').builtinSource`
  and then generate a C++ file containing static char arrays of the
  code cache, using a format similar to `node_javascript.cc`
3. Run `configure` with the `--code-cache-path` option so that
  the newly generated C++ file will be used when compiling the
  new binary. The generated C++ file will put the cache into
  the `internalBinding('code_cache')` object with the module
  ids as keys
4. The new binary tries to read the code cache from
  `internalBinding('code_cache')` and use it to compile
  builtin modules. If the cache is used, it will put the id
  into `require('internal/bootstrap/cache').compiledWithCache`
  for bookkeeping, otherwise the id will be pushed into
  `require('internal/bootstrap/cache').compiledWithoutCache`

This patch also added tests that verify the code cache is
generated and used when compiling builtin modules.

The binary with code cache:

- Is ~1MB bigger than the binary without code cahe
- Consumes ~1MB less memory during start up
- Starts up about 60% faster