Add an automatically-generated "tensorflow.python.platform.build_info" script.

The motivation for this script is to provide better tools for
diagnosing load-time errors (such as the ones that plague the Windows
build due to DLL issues). Note that the script is intended to be
self-contained, so that it is possible to import it without loading
the entire TensorFlow runtime.

This generated script currently contains a single symbol,
`is_cuda_build`, which records whether the build has GPU support or not.

PiperOrigin-RevId: 168471034