When a new process reattaches to OPcache, tracing JIT causes segfaults,
because each new process allocates its own `zend_jit_traces` and
`zend_jit_exit_groups` in SHM, although these need to be shared between
all processes.
We solve that by only allocating these structs for the first process,
and store the pointers in `accel_shared_globals`, so we can reassign
them when a new process reattaches.
Closes GH-7776.
49380b59d2