okl4: declare read-write-lock as volatile

GCC 4.7.4 and newer seems to optimize the lock-variable accesses more
radically, which uncovered the missing volatile qualifier and resulted
in:

Assertion "(int)locked >= 0" failed in file '.../okl4_x86/kernel/include/kernel/read_write_lock.h', line 151 (fn=f0104771)
--- "KD# assert" ---

repos/base-okl4/patches/read_write_lock_volatile.patch

@@ -0,0 +1,13 @@
+diff --git a/pistachio/include/read_write_lock.h b/pistachio/include/read_write_lock.h
+index d667451..49f7f30 100644
+--- a/pistachio/include/read_write_lock.h
++++ b/pistachio/include/read_write_lock.h
+@@ -123,7 +123,7 @@ struct read_write_lock_t
+     bool is_locked(void);
+ 
+ #if defined(CONFIG_DEBUG)
+-    word_t locked;
++    word_t volatile locked;
+ #endif
+ };
+