rework this block to:

```python
if LooseVersion(self.version) < LooseVersion('3.3'):
    clang_src_dir = 'clang-%s.src' % self.version
else:
    clang_src_dir = 'cfe-%s.src' % self.version
src_dirs[clang_src_dir] = os.path.join(self.llvm_src_dir, 'tools', 'clang')
```