Add Pythonic language binding wrapper generation script.

This is only used by Xcode at the moment.  It replaces the
buildSwigWrapperClasses.py and related per-script-language
scripts.  It also fixes a couple bugs in those w/r/t Xcode
usage:

* the presence of the GCC_PREPROCESSOR_DEFINITIONS env var
  should not be short-circuiting generation of the language
  binding; rather, only if LLDB_DISABLE_PYTHON is present
  within that environment variable.

* some logic around what to do when building in "non-Makefile"
  mode.  I've switched the handling of that to be on a
  "--framework" flag - if specified, we build an OS X-style
  framework; otherwise, we go with non.

Putting this up now only attached to the Xcode build so
others can look at it but not be affected by it yet.
After this, I'll tackle the finalizer, along with trying
it locally on Linux.

llvm-svn: 253317