more sparse cleanups

* less-commonly compiled things like ao/mvp outputs
* Adding -Wno-transparent-union to SPARSE_FLAGS makes it check
inside decode.c, directory.c, player.c, and sig_handlers.c
* remove unused variables leftover from the master process
in sig_handlers.c

git-svn-id: https://svn.musicpd.org/mpd/trunk@4598 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/audioOutputs/audioOutput_ao.c

@@ -38,7 +38,7 @@ typedef struct _AoData {
 	ao_device *device;
 } AoData;
 
-static AoData *newAoData()
+static AoData *newAoData(void)
 {
 	AoData *ret = malloc(sizeof(AoData));
 	ret->device = NULL;
@@ -47,7 +47,7 @@ static AoData *newAoData()
 	return ret;
 }
 
-static void audioOutputAo_error()
+static void audioOutputAo_error(void)
 {
 	if (errno == AO_ENOTLIVE) {
 		ERROR("not a live ao device\n");

src/audioOutputs/audioOutput_mvp.c

@@ -90,7 +90,7 @@ static int pcmfrequencies[][3] = {
 
 static int numfrequencies = sizeof(pcmfrequencies) / 12;
 
-static int mvp_testDefault()
+static int mvp_testDefault(void)
 {
 	int fd;