add proper locking for libfmt!

src/lib9/fmtlock2.c

@@ -0,0 +1,16 @@
+#include <u.h>
+#include <libc.h>
+
+static QLock fmtlock;
+
+void
+__fmtlock(void)
+{
+	qlock(&fmtlock);
+}
+
+void
+__fmtunlock(void)
+{
+	qunlock(&fmtlock);
+}