Remove structure magic, because 1) it is no longer conditional, and 2)
it stopped being very effective at detecting memory corruption several
years ago.
Convert configuration-related cpp conditional logic to use static
constant variables, e.g.:
#ifdef JEMALLOC_DEBUG
[...]
#endif
becomes:
if (config_debug) {
[...]
}
The advantage is clearer, more concise code. The main disadvantage is
that data structures no longer have conditionally defined fields, so
they pay the cost of all fields regardless of whether they are used. In
practice, this is only a minor concern; config_stats will go away in an
upcoming change, and config_prof is the only other major feature that
depends on more than a few special-purpose fields.
Properly handle boundary conditions for sampled region promotion in
rallocm(). Prior to this fix, some combinations of 'size' and 'extra'
values could cause erroneous behavior. Additionally, size class
recording for promoted regions was incorrect.
Fix assertions in arena_purge() to accurately reflect the constraints in
arena_maybe_purge(). There were two bugs here, one of which merely
weakened the assertion, and the other of which referred to an
uninitialized variable (typo; used npurgatory instead of
arena->npurgatory).
