make some data extern C and const

RtAudio.cpp

@@ -118,7 +118,7 @@ const unsigned int rtaudio_num_api_names =
 
 // The order here will control the order of RtAudio's API search in
 // the constructor.
-RtAudio::Api rtaudio_compiled_apis[] = {
+extern "C" const RtAudio::Api rtaudio_compiled_apis[] = {
 #if defined(__UNIX_JACK__)
   RtAudio::UNIX_JACK,
 #endif
@@ -148,7 +148,7 @@ RtAudio::Api rtaudio_compiled_apis[] = {
 #endif
   RtAudio::UNSPECIFIED,
 };
-const unsigned int rtaudio_num_compiled_apis =
+extern "C" const unsigned int rtaudio_num_compiled_apis =
   sizeof(rtaudio_compiled_apis)/sizeof(rtaudio_compiled_apis[0])-1;
 }
 

rtaudio_c.cpp

@@ -18,7 +18,7 @@ struct rtaudio {
 const char *rtaudio_version() { return RTAUDIO_VERSION; }
 
 extern "C" const rtaudio_api_t rtaudio_compiled_apis[]; // casting from RtAudio::Api[]
-extern "C" unsigned int rtaudio_num_compiled_apis;
+extern "C" const unsigned int rtaudio_num_compiled_apis;
 const rtaudio_api_t *rtaudio_compiled_api() { return rtaudio_compiled_apis; }
 
 extern "C" const char* rtaudio_api_names[][2];