pthread and synccall cleanup, new __synccall_wait op

fix up clone signature to match the actual behavior. the new
__syncall_wait function allows a __synccall callback to wait for other
threads to continue without returning, so that it can resume action
after the caller finishes. this interface could be made significantly
more general/powerful with minimal effort, but i'll wait to do that
until it's actually useful for something.

src/internal/libc.h

@@ -41,6 +41,7 @@ void __unlockfile(FILE *);
 #define UNLOCK(x) (*(volatile int *)(x)=0)
 
 void __synccall(void (*)(void *), void *);
+void __synccall_wait(void);
 int __setxid(int, int, int, int);
 
 extern char **__environ;

src/internal/pthread_impl.h

@@ -87,6 +87,7 @@ struct __timer {
 
 pthread_t __pthread_self_init(void);
 
+int __uniclone(void *, void (*)(pthread_t), void *);
 int __set_thread_area(void *);
 int __libc_sigaction(int, const struct sigaction *, struct sigaction *);
 int __libc_sigprocmask(int, const sigset_t *, sigset_t *);

src/thread/pthread_create.c

@@ -52,17 +52,13 @@ void __pthread_do_unregister(struct __ptcb *cb)
 	self->cancelbuf = self->cancelbuf->__next;
 }
 
-static int start(void *p)
+static void start(pthread_t self)
 {
-	struct pthread *self = p;
 	if (self->unblock_cancel)
 		__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK, SIGPT_SET, 0, 8);
 	pthread_exit(self->start(self->start_arg));
-	return 0;
 }
 
-int __uniclone(void *, int (*)(), void *);
-
 #define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)
 
 /* pthread_key_create.c overrides this */

src/thread/synccall.c

@@ -4,7 +4,7 @@
 static struct chain {
 	struct chain *next;
 	sem_t sem, sem2;
-} *head;
+} *head, *cur;
 
 static void (*callback)(void *), *context;
 static int chainlen;
@@ -47,11 +47,19 @@ static void handler(int sig, siginfo_t *si, void *ctx)
 	errno = old_errno;
 }
 
+void __synccall_wait()
+{
+	struct chain *ch = cur;
+	sem_post(&ch->sem2);
+	while (sem_wait(&ch->sem));
+	sem_post(&ch->sem);
+}
+
 void __synccall(void (*func)(void *), void *ctx)
 {
 	pthread_t self;
 	struct sigaction sa;
-	struct chain *cur, *next;
+	struct chain *next;
 	uint64_t oldmask;
 
 	if (!libc.threads_minus_1) {