Split time functions into rs_time.rsh header.

Change-Id: I598b0031d15749c91d11fbd37b075d0564a94dbf
diff --git a/libs/rs/rsContext.h b/libs/rs/rsContext.h
index 3c402c4..df275bc 100644
--- a/libs/rs/rsContext.h
+++ b/libs/rs/rsContext.h
@@ -75,6 +75,8 @@
     static uint32_t gThreadTLSKeyCount;
     static uint32_t gGLContextCount;
     static pthread_mutex_t gInitMutex;
+    // Library mutex (for providing thread-safe calls from the runtime)
+    static pthread_mutex_t gLibMutex;
 
     struct ScriptTLSStruct {
         Context * mContext;