$(lldb -P)/../../ is assumed to be the lldb library directory
by the test suite. However, it is possible that the python
libs would be installed in build/lib64 instead of build/lib.
Since liblldb.so is always installed in lib,
make sure this is always used as LLDB_LIB_DIR.
In cases where the python libs were already in build/lib, this
patch will not affect LLDB_LIB_DIR.