Refactor code around JIT creation.

- Create the JIT early on.
- Have dedicated zygote spaces, that get assign after the fork.
- Re-parse compiler options after fork to take into account customization
  of debug flags by the child.

Currently, we only create the thread pool in the child, so the zygote
isn't jitting yet.

Bug: 119800099
Test: test.py, device boots
Change-Id: I591ce933ebf54a67937ab1d05206534f55ef2f65