Convert mutexes, condition vars to statically-allocated tc16

* libguile/scm.h: Add statically allocated tc16s for condvars and
mutexes.
* libguile/threads.c: Adapt to declare tag inline to struct scm_cond and
struct scm_mutex.
* libguile/threads.h: Expose printing procedures internally.
* module/oop/goops.scm:
* libguile/goops.c: Fix to statically allocate condition variable and
mutex classes.
* libguile/eq.c:
* libguile/print.c: Adapt.

module/oop/goops.scm

@@ -71,6 +71,7 @@
             <fluid> <dynamic-state> <frame> <vm> <vm-continuation>
             <keyword> <syntax> <atomic-box> <thread> <bitvector>
             <finalizer> <ephemeron> <ephemeron-table> <character-set>
+            <mutex> <condition-variable>
 
             ;; Numbers.
             <number> <complex> <real> <integer> <fraction>
@@ -82,7 +83,7 @@
             ;; corresponding classes, which may be obtained via class-of,
             ;; once you have an instance.  Perhaps FIXME to provide a
             ;; smob-type-name->class procedure.
-            <promise> <mutex> <condition-variable>
+            <promise>
             <regexp> <hook> <random-state>
             <directory> <array>
             <dynamic-object> <macro>
@@ -1083,6 +1084,8 @@ slots as we go."
 (define-standard-class <ephemeron> (<top>))
 (define-standard-class <ephemeron-table> (<top>))
 (define-standard-class <character-set> (<top>))
+(define-standard-class <condition-variable> (<top>))
+(define-standard-class <mutex> (<top>))
 (define-standard-class <thread> (<top>))
 (define-standard-class <number> (<top>))
 (define-standard-class <complex> (<number>))
@@ -3531,8 +3534,6 @@ var{initargs}."
 ;;;
 
 (define <promise> (find-subclass <top> '<promise>))
-(define <mutex> (find-subclass <top> '<mutex>))
-(define <condition-variable> (find-subclass <top> '<condition-variable>))
 (define <regexp> (find-subclass <top> '<regexp>))
 (define <hook> (find-subclass <top> '<hook>))
 (define <bitvector> (find-subclass <top> '<bitvector>))