6fa2d21ba5
- according to man.openbsd.org getentropy() is in unistd.h
- according to macOS sierra's man it's in sys/random.h
- since sys/random.h is does not exist for iOS and for linux, do
not attempt to include it, rather redeclare the prototype
- make sure that `./configure`:
- uses getentropy() on macOS sierra
- does not use getentropy() if compiling for 10.11
- does not use getentropy() if compiling for ios armv7