So scale-amd64 can build lwIP again..

This have to do with implementation, not interface.  Removing these
unmasks the sharing on tlbflush_req, which is something we expected.
Luckily, it doesn't expose any other sharing.

Load indirect array on demand and flush only on iupdate.

This eliminates all reports of unexpected sharing except a few cases
of honest-to-goodness memory reuse.

Mostly to make sure what I just did works.

This works by lazily allocating a lock's klockstat structure when the
lock is first acquired.

These safety policies help ensure that an accessor does not migrate
CPUs while accessing a percpu variable.  The "cli" safety policy only
allows percpu variables to be accessed when interrupts are disabled.
The "internal" safety policy leaves it up to the caller.  Not
surprisingly, most current percpu variables use internal.

These locks can be statically constructed in the .data segment, since
the constructor is constexpr.  Currently this only works for locks
that aren't tracked by lockstat.