Fix swig python package path

Summary:
The path defined in CMakeLists.txt doesn't match the path generated in
our python script. This change fixes that.

LLVM_LIBRARY_OUTPUT_INTDIR is defined as:

${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})

On the other hand, the path of site-package is generaged in
get_framework_python_dir_windows() in finishSwigPythonLLDB.py as:
(Dispite its name, the function is used for everything other than xcode)

prefix/cmakeBuildConfiguration/distutils.sysconfig.get_python_lib()

From lldb/CMakeLists.txt, we can see that:
prefix=${CMAKE_BINARY_DIR},
cmakeBuildConfiguration=${CMAKE_CFG_INTDIR}

And from python source code, we can see get_python_lib() always returns
lib/pythonx.y/site-packages for posix, or Lib/site-packages for windows:
https://github.com/python/cpython/blob/3.8/Lib/distutils/sysconfig.py#L128

We should make them match each other.

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D67583

llvm-svn: 372047