minor fix for OSX and update travis using ccache to speed up compilation

.travis.yml

@@ -1,5 +1,7 @@
 language: cpp
 
+# cache results
+
 # Currently sudo is not required, NO ENV is used 
 
 # Supported Operating systems

CMakeLists.txt

@@ -1,5 +1,11 @@
 cmake_minimum_required(VERSION 2.8.12)
 
+find_program(CCACHE_FOUND ccache)
+if(CCACHE_FOUND)
+        set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
+        set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
+endif(CCACHE_FOUND)
+
 if (${CMAKE_VERSION} VERSION_GREATER "3.8")
     #For cmake >= 3.9 INTERPROCEDURAL_OPTIMIZATION behaviour we need to explicitly
     #set the cmake policy version number

vpr7_x2p/vpr/SRC/device/mux_graph.cpp

@@ -610,7 +610,7 @@ void MuxGraph::build_mux_graph(const CircuitLibrary& circuit_lib,
   default:
     vpr_printf(TIO_MESSAGE_ERROR, 
                "(File:%s, [LINE%d]) Invalid multiplexer structure for circuit model (name=%s)!\n",
-              __FILE__, __LINE__, circuit_lib.model_name(circuit_model));
+              __FILE__, __LINE__, circuit_lib.model_name(circuit_model).c_str());
     exit(1);
   }