Add ndk-gdb script to the NDK.

Add ndk-gdb script to the NDK.

This is a helper script used to launch a native debugging session.
To use it, follow these steps:

1. Make your application debuggable
2. Build the machine code with 'ndk-build'  (make APP=<name> is not supported)
3. Build the package with ant or the ADT Eclipse plugin
4. Install it on your device/emulator
5. Launch it
6. Run 'ndk-gdb' from your application project directory.

Change-Id: Ie3b0557e70cefa0080075a34ad0ca46bebef3c42
NOTE: To work properly, a modified gdbserver binary must be used
      (one that binds to Unix sockets instead of TCP ones). Patch
      upcoming.