Uncommenting the following line in `Modules/Setup` leads to a compiler error on macOS (tested w/ Xcode 10):

```
./Modules/expat/xmlparse.c:92:3: error: You do not have support for any sources of high quality entropy enabled. For end user security, that is probably not what you want.
      Your options include: * Linux + glibc >=2.25 (getrandom): HAVE_GETRANDOM, * Linux + glibc <2.25 (syscall SYS_getrandom): HAVE_SYSCALL_GETRANDOM, * BSD / macOS >=10.7
      (arc4random_buf): HAVE_ARC4RANDOM_BUF, * BSD / macOS <10.7 (arc4random): HAVE_ARC4RANDOM, * libbsd (arc4random_buf): HAVE_ARC4RANDOM_BUF + HAVE_LIBBSD, * libbsd
      (arc4random): HAVE_ARC4RANDOM + HAVE_LIBBSD, * Linux / BSD / macOS (/dev/urandom): XML_DEV_URANDOM * Windows (RtlGenRandom): _WIN32. If insist on not using any of
      these, bypass this error by defining XML_POOR_ENTROPY; you have been warned. If you have reasons to patch this detection code away or need changes to the build system,
      please open a bug. Thank you!
```

I believe this is due to `setup.py` being out of sync with `Modules/Setup`, which defines `XML_POOR_ENTROPY`. I'll attach a patch that resolves the issue for me.