AAT::Lookup has no other way to detect whether it is returned from
a real and sanitized font data or from a null pool, this checks if
the table has been recognized valid by sanitizer by checking
table's major version which is zero if returned from a null pool and
non-zero if is from a sanitized font data, it is expected the other
calls of the table (unlikely to have more calls however) also do a
similar version check before calling the lookups used on the table.
Include stdbool.h in hb-setset-test.h instead of in the individual
sources, if it is found; otherwise use a simplistic fallback for it if
it is not found.
Also declare variables at the top of the block, to build on pre-C99
compiliers.