* libguile/scm.h (scm_tc7_thread): Give threads their own tc7.
* libguile/threads.h (struct scm_thread): Add a tag, so that struct
thread can be a SCM directly. Add a struct gc_mutator* member.
(scm_thread_handle): New inline function.
(SCM_I_IS_THREAD, SCM_I_THREAD_DATA, SCM_VALIDATE_THREAD): Update to use
tc7 instead of SMOB tags.
* libguile/continuations.c (scm_i_with_continuation_barrier)
* libguile/finalizers.c (queue_finalizer_async)
* libguile/jit.c (compile_current_thread)
* libguile/threads.c (block_self, guilify_self_2)
(lock_mutex, unlock_mutex, timed_wait scm_current_thread)
(scm_all_threads)
* libguile/vm-engine.c (current-thread): Use scm_thread_handle instead
of thread->handle.
* libguile/evalext.c (scm_self_evaluating_p):
* libguile/goops.c (class_thread, scm_class_of, scm_sys_goops_early_init)
* libguile/print.c (iprin1)
* module/language/cps/compile-bytecode.scm (compile-function)
* module/oop/goops.scm (<thread>)
* module/system/base/types.scm (cell->object)
* module/system/base/types/internal.scm (heap-tags)
* module/system/vm/assembler.scm: (emit-thread?): Adapt to
scm_tc7_thread.
* libguile/gc-internal.h: Move init functions that take "struct
gc_stack_addr" here, so that internal Whippet uses don't cause Whippet
to be added to public headers.
* libguile/gc.c (scm_storage_prehistory): Take struct gc_stack_addr as
arg, and pass to gc_init. Return a mutator pointer.
* libguile/init.c (scm_i_init_guile): Pass mutator and stack base to GC
and thread init routines.
* libguile/threads.c (scm_trace_dynstack, scm_trace_thread)
(scm_trace_thread_mutator_roots): New infra for marking threads in terms
of Whippet API.
* libguile/threads.c (guilify_self_1): Since we don't use a separate GC
kind for threads any more, and thread marking is keyed off
gc_mutator_set_roots, we can avoid some of the gnarly synchronization.
(on_thread_exit): Arrange to gc_finish_for_thread.
(scm_i_init_thread_for_guile): Use gc_init_for_thread.
(init_main_thread, with_guile, scm_i_with_guile): Use Whippet API.
(scm_threads_prehistory): Take main-thread mutator and the stack base as
arguments.
* libguile/vm.c (scm_trace_vm): Rework in terms of Whippet API.
* libguile/whippet-embedder.h (gc_trace_mutator_roots): Arrange to trace
the current mutator's SCM thread object.
* libguile/trace.h: New file, to declare implementations of trace
routines.
* libguile/Makefile.am (noinst_HEADERS): Add trace.h.
* configure.ac: Add subdir-objects Makefile.am option, to prevent
accidental collision between object file names.
* libguile/Makefile.am: Include whippet/embed.am, and add the
appropriate hooks to the Makefile.
* libguile/whippet-embedder.h: New file.
