Enable and fix -Wunused-parameter warnings.

configure.ac

 
 AX_CHECK_COMPILE_FLAG([-Wunused-function], [CFLAGS="-Wunused-function $CFLAGS"])
 
+AX_CHECK_COMPILE_FLAG([-Wunused-parameter], [CFLAGS="-Wunused-parameter $CFLAGS"])
+
 dnl ================================================================
 dnl Generate output.
 dnl ================================================================

src/libespeak-ng/encoding.c

 static uint32_t
 null_decoder_getc(espeak_ng_TEXT_DECODER *decoder)
 {
+	(void)decoder; // unused parameter
 	return 0;
 }
 

src/libespeak-ng/synth_mbrola.c

 
 espeak_ng_STATUS LoadMbrolaTable(const char *mbrola_voice, const char *phtrans, int *srate)
 {
+	(void)mbrola_voice; // unused parameter
+	(void)phtrans; // unused parameter
+	(void)srate; // unused parameter
 	return ENS_NOT_SUPPORTED;
 }
 
 int MbrolaGenerate(PHONEME_LIST *phoneme_list, int *n_ph, int resume)
 {
+	(void)phoneme_list; // unused parameter
+	(void)n_ph; // unused parameter
+	(void)resume; // unused parameter
 	return 0;
 }
 
 int MbrolaFill(int length, int resume, int amplitude)
 {
+	(void)length; // unused parameter
+	(void)resume; // unused parameter
+	(void)amplitude; // unused parameter
 	return 0;
 }
 

tests/api.c

 int
 main(int argc, char **argv)
 {
+	(void)argc; // unused parameter
+
 	char *progdir = strdup(argv[0]);
 	char *dir = strrchr(progdir, '/');
 	if (dir != NULL) *dir = 0;

tests/encoding.c

 int
 main(int argc, char **argv)
 {
+	(void)argc; // unused parameter
+	(void)argv; // unused parameter
+
 	test_unbound_text_decoder();
 	test_unknown_encoding();
 

tests/readclause.c

 int
 main(int argc, char **argv)
 {
+	(void)argc; // unused parameter
+	(void)argv; // unused parameter
+
 	assert(espeak_Initialize(AUDIO_OUTPUT_SYNCHRONOUS, 0, NULL, espeakINITIALIZE_DONT_EXIT) == 22050);
 
 	test_latin();