dlopen failed: cannot locate symbol "__register_atfork" on Android 5.0

[obfusk]

Checklist

• [x] the issue is indeed a bug and not a support request
• [x] issue doesn't already exist: https://github.com/kivy/python-for-android/issues
• [ ] I have a short, runnable example that reproduces the issue
• [x] I reproduced the problem with the latest development version (p4a.branch = develop)
• [x] I used the grave accent (aka backticks) to format code or logs when appropriated

Description

The Google Play pre-launch report for my app shows the following error on a Huawei P8 青春版 (Android 5.0 (SDK 21)):

dlopen failed: cannot locate symbol "__register_atfork" referenced by "/data/app/my.app-1/lib/arm64/libmain.so"...

This makes sense since __register_atfork is only available in API level >= 23.

AFAIK Python doesn't use atfork, but OpenSSL does; I assume that's the issue.