rtaudio_c: add rtaudio_num_compiled_api()

rtaudio_c.cpp

@@ -22,6 +22,11 @@ const rtaudio_api_t *rtaudio_compiled_api() {
   return (rtaudio_api_t *) &rtaudio_compiled_apis[0];
 }
 
+extern "C" const unsigned int rtaudio_num_compiled_apis;
+const unsigned int rtaudio_num_compiled_api(void) {
+  return rtaudio_num_compiled_apis;
+}
+
 extern "C" const char* rtaudio_api_names[][2];
 const char *rtaudio_api_name(rtaudio_api_t api) {
     if (api < 0 || api >= RTAUDIO_API_NUM)

rtaudio_c.h

@@ -106,6 +106,7 @@ typedef struct rtaudio_stream_options {
 typedef struct rtaudio *rtaudio_t;
 
 RTAUDIOAPI const char *rtaudio_version(void);
+RTAUDIOAPI const unsigned int rtaudio_num_compiled_api(void);
 RTAUDIOAPI const rtaudio_api_t *rtaudio_compiled_api(void);
 RTAUDIOAPI const char *rtaudio_api_name(rtaudio_api_t api);
 RTAUDIOAPI const char *rtaudio_api_display_name(rtaudio_api_t api);