Make fork() go 30% faster

This change makes fork() go nearly as fast as sys_fork() on UNIX. As for
Windows this change shaves about 4-5ms off fork() + wait() latency. This
is accomplished by using WriteProcessMemory() from the parent process to
setup the address space of a suspended process; it is better than a pipe

third_party/nsync/common.c

@@ -238,7 +238,8 @@ static bool free_waiters_populate (void) {
 		// netbsd semaphores are file descriptors
 		n = 1;
 	} else {
-		n = __pagesize / sizeof(waiter);
+		// don't create too much fork() overhead
+		n = 16;
 	}
 	waiter *waiters = mmap (0, n * sizeof(waiter),
 				PROT_READ | PROT_WRITE,