Don't compile scripts directory if LLDB_DISABLE_PYTHON is set

Summary:
What looks like a typo has caused the scripts/Python directory to be compiled on non-Windows
platforms even with LLDB_DISABLE_PYTHON, which failed if Python.h was unavaiable. This changes
the condition to avoid compilation if LLDB_DISABLE_PYTHON is set.

Test Plan: Remove Python.h, verify compilation is successful.

Reviewers: zturner

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8855

llvm-svn: 234319