Implement espeak_SetVoiceByProperties directly from the SetVoiceByProperties implementation.

src/libespeak-ng/espeak_command.c

 	case ET_VOICE_SPEC:
 	{
 		espeak_VOICE *data = &(the_command->u.my_voice_spec);
-		SetVoiceByProperties(data);
+		espeak_SetVoiceByProperties(data);
 	}
 		break;
 	default:

src/libespeak-ng/espeak_command.h

 void sync_espeak_SetParameter(espeak_PARAMETER parameter, int value, int relative);
 int sync_espeak_SetVoiceByName(const char *name);
 int sync_espeak_SetVoiceByProperties(espeak_VOICE *voice_selector);
-espeak_ERROR SetVoiceByProperties(espeak_VOICE *voice_selector);
 void SetParameter(int parameter, int value, int relative);
 
 int sync_espeak_terminated_msg(unsigned int unique_identifier, void *user_data);

src/libespeak-ng/speak_lib.c

 #endif
 }
 
-ESPEAK_API espeak_ERROR espeak_SetVoiceByProperties(espeak_VOICE *voice_selector)
-{
-	return SetVoiceByProperties(voice_selector);
-}
-
 ESPEAK_API int espeak_GetParameter(espeak_PARAMETER parameter, int current)
 {
 	// current: 0=default value, 1=current value

src/libespeak-ng/synthesize.h

 extern int n_soundicon_tab;
 extern SOUND_ICON soundicon_tab[N_SOUNDICON_TAB];
 
-espeak_ERROR SetVoiceByProperties(espeak_VOICE *voice_selector);
 espeak_ERROR LoadMbrolaTable(const char *mbrola_voice, const char *phtrans, int *srate);
 void SetParameter(int parameter, int value, int relative);
 int MbrolaTranslate(PHONEME_LIST *plist, int n_phonemes, int resume, FILE *f_mbrola);

src/libespeak-ng/voices.c

 	return EE_INTERNAL_ERROR; // voice name not found
 }
 
-#pragma GCC visibility pop
-
-espeak_ERROR SetVoiceByProperties(espeak_VOICE *voice_selector)
+espeak_ERROR espeak_SetVoiceByProperties(espeak_VOICE *voice_selector)
 {
 	const char *voice_id;
 	int voice_found;
 	return EE_OK;
 }
 
+#pragma GCC visibility pop
+
 void FreeVoiceList()
 {
 	int ix;

src/speak-ng.c

 	if (espeak_SetVoiceByName(voicename) != EE_OK) {
 		memset(&voice_select, 0, sizeof(voice_select));
 		voice_select.languages = voicename;
-		if (SetVoiceByProperties(&voice_select) != EE_OK) {
+		if (espeak_SetVoiceByProperties(&voice_select) != EE_OK) {
 			fprintf(stderr, "%svoice '%s'\n", err_load, voicename);
 			exit(2);
 		}