MFC 295636,295637:
Fix issues with tracing Linux/i386 binaries.

295636:
Sign extend the error value for failing Linux/i386 system calls. This
restores the mapping of Linux errors to native FreeBSD errno values after
the refactoring in r288424.

295637:
Correct the ABI name for Linux/i386 binaries under FreeBSD/i386.

This allows truss to work for these binaries again after r288424.

Approved by: re (marius)