[CMake] On Windows fix the ``install`` target so that it installs ``libz3.dll``.
[CMake] On Windows fix the ``install`` target so that it installs
``libz3.dll``.

I've left a comment about the installation of ``libz3.lib``. I'm not
sure if we want that installed or not.

seahorn/z3,kyledewey/z3,kyledewey/z3,seahorn/z3,seahorn/z3,kyledewey/z3,kyledewey/z3,seahorn/z3,kyledewey/z3,kyledewey/z3,seahorn/z3,seahorn/z3