kernel - Try harder to unmount a filesystem

* Use LK_TIMELOCK (5 seconds) instead of LK_NOWAIT when getting the mp
  lockmgr lock for unforced unmounts.

* Remove the syncer vnode and issue VFS_SYNC prior to checking
  mnt_refs instead of after the check.  This appears to improve tmpfs's
  chances of unmounting, though it is a bit unclear as to why.

* Wait up to 1 second for mnt_refs to drop to 1 before giving up.

* Improves Poudriere's chances of successfully unmounting a tmpfs
  filesystem.
gcc47/x86_64: Add more -mno flags
Revert "<malloc.h>: Restrict support for <malloc.h> to !defined(__STDC__)."

This reverts commit 1b3342693b737646f3cab0715e31ec6ab5216b38.

It caused too many issues in the package department.

Reported-by: marino
bce: Move status index's location and cached status index into RX ring
bce: Put interrupt reenabling into each interrupt handlers

So shared interrupt reenabling code do not need to check interrupt
type; only legacy interrupt needs extra register writing.