Unused, but now that we have CrapPool, implement it.

Common Regoin for Access Protection.  Like the NullPool, but writable.

Seems like I messed up; buffer overrun got reported.

X-terminated means don't access this, it's not located correctly.
Z-terminated means this is a C array with no bound checking.

It uses floor implicitly without it but explicit use of round will be more correct.

[subset] fix calculation of range shiftz. Should be 16 * len - searchRange not 16 * (len - searchRange).

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=6022

This one might do it...

If we don't have visibility, make NullPool static.

We keep a separate private NullPool in libharfbuzz-subset.so
This can fire back later since now there are two separate null objects,
and comparisons to the null pool can be confused.  Something to deal
with when it comes up. Ouch!

Such a headache that Windows defines UINT8, ...; Just prefix it.

Untested, but compiles.