setup: conditionalize access to `sys.dllhandle` when building extensions This code is only run on Windows, and was crashing PyOxidizer when running in `setup-py-install` mode. Now an oxidized binary can be built by simply pointing to setup.py. Something is slightly different now that it's not being built from a virtualenv. Previously, `hg version` could print to the screen, but now it aborts saying "Incorrect function". But I can see the output if redirected to a file, and it's not complaining about missing C extensions, so I think those are loading now (unlike from the virtualenv). The interesting this about this incorrect function output is that it failed when initially built. I then went back and did a `make clean` and `make local` with py3 and then py2 to ensure I didn't break the existing code. At that point I ran the oxidized executable again and it was able to print to the screen normally! So I ran `pyoxidizer build` again, it only output the following, and then running the executable failed to output again: (pyO2_venv) C:\Users\Matt\hg3\hg_pyO2>pyoxidizer build Finished dev [unoptimized + debuginfo] target(s) in 0.12s packaging application into C:/Users/Matt/hg3/hg_pyO2\build\apps\hg_pyO2\x86_64-pc-windows-msvc\debug purging C:/Users/Matt/hg3/hg_pyO2\build\apps\hg_pyO2\x86_64-pc-windows-msvc\debug copying C:/Users/Matt/hg3/hg_pyO2\build\target\x86_64-pc-windows-msvc\debug\hg_pyO2.exe to C:/Users/Matt/hg3/hg_pyO2\build\apps\hg_pyO2\x86_64-pc-windows-msvc\debug\hg_pyO2.exe resolving packaging state... writing license for [...] hg_pyO2 packaged into C:/Users/Matt/hg3/hg_pyO2\build\apps\hg_pyO2\x86_64-pc-windows-msvc\debug executable path: C:/Users/Matt/hg3/hg_pyO2\build\apps\hg_pyO2\x86_64-pc-windows-msvc\debug\hg_pyO2.exe Differential Revision: https://phab.mercurial-scm.org/D7444