Create an _d suffixed symlink when doing a debug Windows build.

_lldb is built as an extension module on Windows.  Normally to load
an extension module named 'foo', Python would look for the file
'foo.pyd'.  However, when a debug interpreter is used, Python will
look for the file 'foo_d.pyd'.  This change checks the build
configuration and creates the correct symlink name based on the
build configuration.