for c11 mtx and cnd functions, use externally consistent type names

despite looking like undefined behavior, the affected code is correct
both before and after this patch. the pairs mtx_t and pthread_mutex_t,
and cnd_t and pthread_cond_t, are not mutually compatible within a
single translation unit (because they are distinct untagged aggregate
instances), but they are compatible with an object of either type from
another translation unit (6.2.7 ¶1), and therefore a given translation
unit can choose which one it wants to use.

in the interest of being able to move declarations out of source files
to headers that facilitate checking, use the pthread type names in
declaring the namespace-safe versions of the pthread functions and
cast the argument pointer types when calling them.

src/thread/cnd_broadcast.c

@@ -1,10 +1,11 @@
 #include <threads.h>
+#include <pthread.h>
 
-int __private_cond_signal(cnd_t *, int);
+int __private_cond_signal(pthread_cond_t *, int);
 
 int cnd_broadcast(cnd_t *c)
 {
 	/* This internal function never fails, and always returns zero,
 	 * which matches the value thrd_success is defined with. */
-	return __private_cond_signal(c, -1);
+	return __private_cond_signal((pthread_cond_t *)c, -1);
 }

src/thread/cnd_signal.c

@@ -1,10 +1,11 @@
 #include <threads.h>
+#include <pthread.h>
 
-int __private_cond_signal(cnd_t *, int);
+int __private_cond_signal(pthread_cond_t *, int);
 
 int cnd_signal(cnd_t *c)
 {
 	/* This internal function never fails, and always returns zero,
 	 * which matches the value thrd_success is defined with. */
-	return __private_cond_signal(c, 1);
+	return __private_cond_signal((pthread_cond_t *)c, 1);
 }

src/thread/cnd_timedwait.c

@@ -1,11 +1,12 @@
 #include <threads.h>
+#include <pthread.h>
 #include <errno.h>
 
-int __pthread_cond_timedwait(cnd_t *restrict, mtx_t *restrict, const struct timespec *restrict);
+int __pthread_cond_timedwait(pthread_cond_t *restrict, pthread_mutex_t *restrict, const struct timespec *restrict);
 
 int cnd_timedwait(cnd_t *restrict c, mtx_t *restrict m, const struct timespec *restrict ts)
 {
-	int ret = __pthread_cond_timedwait(c, m, ts);
+	int ret = __pthread_cond_timedwait((pthread_cond_t *)c, (pthread_mutex_t *)m, ts);
 	switch (ret) {
 	/* May also return EINVAL or EPERM. */
 	default:        return thrd_error;

src/thread/mtx_timedlock.c

@@ -1,11 +1,12 @@
 #include <threads.h>
+#include <pthread.h>
 #include <errno.h>
 
-int __pthread_mutex_timedlock(mtx_t *restrict, const struct timespec *restrict);
+int __pthread_mutex_timedlock(pthread_mutex_t *restrict, const struct timespec *restrict);
 
 int mtx_timedlock(mtx_t *restrict m, const struct timespec *restrict ts)
 {
-	int ret = __pthread_mutex_timedlock(m, ts);
+	int ret = __pthread_mutex_timedlock((pthread_mutex_t *)m, ts);
 	switch (ret) {
 	default:        return thrd_error;
 	case 0:         return thrd_success;

src/thread/mtx_trylock.c

@@ -1,14 +1,14 @@
 #include "pthread_impl.h"
 #include <threads.h>
 
-int __pthread_mutex_trylock(mtx_t *);
+int __pthread_mutex_trylock(pthread_mutex_t *);
 
 int mtx_trylock(mtx_t *m)
 {
 	if (m->_m_type == PTHREAD_MUTEX_NORMAL)
 		return (a_cas(&m->_m_lock, 0, EBUSY) & EBUSY) ? thrd_busy : thrd_success;
 
-	int ret = __pthread_mutex_trylock(m);
+	int ret = __pthread_mutex_trylock((pthread_mutex_t *)m);
 	switch (ret) {
 	default:    return thrd_error;
 	case 0:     return thrd_success;

src/thread/mtx_unlock.c

@@ -1,11 +1,12 @@
 #include <threads.h>
+#include <pthread.h>
 
-int __pthread_mutex_unlock(mtx_t *);
+int __pthread_mutex_unlock(pthread_mutex_t *);
 
 int mtx_unlock(mtx_t *mtx)
 {
 	/* The only cases where pthread_mutex_unlock can return an
 	 * error are undefined behavior for C11 mtx_unlock, so we can
 	 * assume it does not return an error and simply tail call. */
-	return __pthread_mutex_unlock(mtx);
+	return __pthread_mutex_unlock((pthread_mutex_t *)mtx);
 }