Make TranslateClause return 'const void *' to preserve constness.

src/libespeak-ng/translate.c

@@ -1926,7 +1926,7 @@ static espeak_ng_STATUS init_string_decoder(const char *text, espeak_ng_ENCODING
 	return text_decoder_decode_string(p_decoder, text, strlen(text) + 1, encoding);
 }
 
-void *TranslateClause(Translator *tr, const void *vp_input, int *tone_out, char **voice_change)
+const void *TranslateClause(Translator *tr, const void *vp_input, int *tone_out, char **voice_change)
 {
 	int ix;
 	int c;

src/libespeak-ng/translate.h

@@ -760,7 +760,7 @@ int Unpronouncable(Translator *tr, char *word, int posn);
 void SetWordStress(Translator *tr, char *output, unsigned int *dictionary_flags, int tonic, int prev_stress);
 int TranslateRules(Translator *tr, char *p, char *phonemes, int size, char *end_phonemes, int end_flags, unsigned int *dict_flags);
 int TranslateWord(Translator *tr, char *word1, WORD_TAB *wtab, char *word_out);
-void *TranslateClause(Translator *tr, const void *vp_input, int *tone, char **voice_change);
+const void *TranslateClause(Translator *tr, const void *vp_input, int *tone, char **voice_change);
 int ReadClause(Translator *tr, char *buf, short *charix, int *charix_top, int n_buf, int *tone_type, char *voice_change);
 
 void SetVoiceStack(espeak_VOICE *v, const char *variant_name);