On AIX, calling mmap on a pre-designated address with
MAP_FIXED will fail and return -1 unless the application
has requested SPEC1170 compliant behaviour with arguments
such as `XPG_SUS_ENV=ON`.

Therefore an AIX specific implementation has been added under
platform-aix.cc.

Change-Id: Ib5b8a19a3a9e6d202aed7e792c00a25ddc547c72
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3403045Reviewed-by: Samuel Groß <saelo@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Milad Farazmand <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#78778}