libc: support using old mmap instead of bionic's mmap

Summary: Setting BOARD_NEEDS_OLD_MMAP is the same as reverting commit afcc0cccdafef0c67600cbbc72cee0e7a41f3f04: "Add mmap64()" for ARM.

Test Plan: @jriordan001 should verify

Reviewers: randall.rushing, raymanfx, anders3408, jriordan001

Reviewed By: jriordan001

Differential Revision: http://review.codefirex.com/D214