[Bug #18382] Fix crash in compaction for
	 ObjectSpace.trace_object_allocations

	ObjectSpace.trace_object_allocations can crash when auto-compaction is
	enabled.
	---
	 ext/objspace/object_tracing.c | 3 ++-
	 1 file changed, 2 insertions(+), 1 deletion(-)

	undefine alloc functions for C extensions

	per guidance in doc/extension.rdoc, these classes now undefine their
	alloc functions:

	- ObjectSpace::InternalObjectWrapper
	- Socket::Ifaddr
	---
	 ext/objspace/objspace.c | 1 +
	 ext/socket/ifaddr.c     | 1 +
	 2 files changed, 2 insertions(+)

	objspace_dump.c: Handle allocation path and line missing

	---
	 ext/objspace/objspace_dump.c | 13 +++++++++----
	 1 file changed, 9 insertions(+), 4 deletions(-)

constant cache `IC` is accessed by non-atomic manner and there are
thread-safety issues, so Ruby 3.0 disables to use const cache on
non-main ractors.

This patch enables it by introducing `imemo_constcache` and allocates
it by every re-fill of const cache like `imemo_callcache`.
[Bug #17510]

Now `IC` only has one entry `IC::entry` and it points to
`iseq_inline_constant_cache_entry`, managed by T_IMEMO object.

`IC` is atomic data structure so `rb_mjit_before_vm_ic_update()` and
`rb_mjit_after_vm_ic_update()` is not needed.

Now we need atomic operations, which are lighter than mutex, more
widely for extension libraries because of Ractor.

This iterator uses an st_table, but if objects move the references in
the st table won't be updated.  This patch just changes the st table to
an identity hash.

RDoc says `ObjectSpace.dump(obj, output: :stdout)   # => nil`,
but it returns STDOUT since fbba6bd4e3dff7a61965208fecae908f10c4edbe.

I think it is unintentional change.

We have code common to all heap iteration paths in this file.  Refactor
such that we keep ASAN checks and flags checks in one place

Again, this code is walking the heap.  Empty slots can be poisoned, so
we need to unpoison before checking the type