Wrapper: use thread local storage from v8::internal

  - I'm using v8::internal TLS implementation since it work on
    android, linux and others.

    This code hasn't been tested in the battlefield, but it should
    fix compile time problems on android and thread safety on Windows.

    TODO: Fix other uses of __thread

Signed-off-by: Camille Moncelier <camille@moncelier.fr>