Various tweaks to make things run on Mac OS.
The main change is the use of pthread to implement ffork.
diff --git a/src/lib9/ffork-FreeBSD.c b/src/lib9/ffork-FreeBSD.c
index a7c82e6..3829bb2 100644
--- a/src/lib9/ffork-FreeBSD.c
+++ b/src/lib9/ffork-FreeBSD.c
@@ -31,3 +31,9 @@
 	lock((Lock*)&lk->access_lock);
 }
 
+int
+getfforkid(void)
+{
+	return getpid();
+}
+