I had introduced it with d83de4b1 in
2012, when the C++/UNO bridge for 64-bit OS X was created mostly as a
copy of the Linux one.

Stephan says that the only need for USE_DOUBLE_MMAP should be on
SELinux anyway, so most likely also its use for the various BSDs and
Android are copypasta or cargo cult.

Change-Id: I1c16e830e5e8269b78b14837a9127a98612a6e54