(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
Allocate GC heap blocks with mmap(MAP_RANDOMIZED) for ASLR.
This may very well be too aggressive in terms of fragmentation, and we
can figure out ways to scale that back once it becomes a big problem.
For now, this makes the GC heap a lot less predictable for an attacker.
