Move a private x86-64 header file out of the limelight.

Currently this is on everyone's include path and is getting exported
via the NDK.

Change-Id: Ia417839fb65c7e0afddcd9fae3438665dae8e752
Merge "Move a private x86-64 header file out of the limelight."
Add error-check when mapping socket to fd

The call to fdopen can fail in several ways.
The fprintf on the next line will then dereference a
NULL-pointer FILE*.
Added a NULL-check, closed the socket, returned system error
and added a comment about it.

Change-Id: I7a6b26aa3c79452b1fdd76af12dfa75da88cbad7
Merge "Add error-check when mapping socket to fd"