reorganize pthread data structures and move the definitions to alltypes.h

this allows sys/types.h to provide the pthread types, as required by
POSIX. this design also facilitates forcing ABI-compatible sizes in
the arch-specific alltypes.h, while eliminating the need for
developers changing the internals of the pthread types to poke around
with arch-specific headers they may not be able to test.

src/thread/pthread_cond_broadcast.c

@@ -2,7 +2,7 @@
 
 int pthread_cond_broadcast(pthread_cond_t *c)
 {
-	c->__block = 0;
-	__wake(&c->__block, -1, 0);
+	c->_c_block = 0;
+	__wake(&c->_c_block, -1, 0);
 	return 0;
 }