fix a few random compiler warnings

 * unused variables
 * implicit enum conversion
 * sigend <-> unsigned comparison
 * left shift negative number

The only warnings left on my setup right now are `-Wstringop-truncation`
from strncpy calls. Those are not trivial to fix. Turns out the code does
regularly not take into account that strncpy may not result in a null
terminated string. Details, see `man string_copying`.

camlibs/ax203/ax203_decode_yuv_delta.c

@@ -43,6 +43,7 @@
 
 #define CLAMP_U8(x) (((x) > 255) ? 255 : (((x) < 0) ? 0 : (x)))
 
+#ifdef HAVE_LIBGD
 static const int corr_tables[4][8] = {
 	/* Table 0 depends on wrap around to get negative
 	   corrections!! */
@@ -52,7 +53,6 @@ static const int corr_tables[4][8] = {
 	{ 0,  4,  8, 12, -16, -12,  -8, -4 },
 };
 
-#ifdef HAVE_LIBGD
 /* With in a compressed 4x4 block, the data is stored 4 component values at a
    time, compressed into 2 bytes, the first 5 bits are a starting value,
    then 2 bits encoding which correction/delta table to use and

camlibs/pentax/pslr.c

@@ -982,7 +982,7 @@ int pslr_set_exposure_mode(pslr_handle_t h, pslr_exposure_mode_t mode) {
     }
 
     if ( p->model->need_exposure_mode_conversion ) {
-        mode = exposure_mode_conversion( mode );
+        mode = (pslr_exposure_mode_t)exposure_mode_conversion( mode );
     }
 
     return ipslr_handle_command_x18( p, true, X18_EXPOSURE_MODE, 2, 1, mode, 0);

camlibs/ptp2/ptp.c

@@ -412,7 +412,7 @@ fd_putfunc(PTPParams* params, void* private,
 	PTPFDHandlerPrivate* priv = (PTPFDHandlerPrivate*)private;
 
 	written = write (priv->fd, data, sendlen);
-	if (written != sendlen)
+	if ((unsigned long)written != sendlen)
 		return PTP_ERROR_IO;
 	return PTP_RC_OK;
 }

camlibs/quicktake1x0/qtkn-decoder.c

@@ -112,7 +112,7 @@ int qtkn_decode(unsigned char *raw, int width, int height, unsigned char **out)
 		for (c=0; c < 3; c++) {
 			val = ((0x1000000/last[c] + 0x7ff) >> 12) * mul[c];
 			s = val > 65564 ? 10:12;
-			x = ~(-1 << (s-1));
+			x = ~((unsigned int)-1 << (s-1));
 			val <<= 12-s;
 			for (i=0; i < (int)(sizeof(buf[0])/sizeof(short)); i++) {
 				((short *)buf[c])[i] = (((short *)buf[c])[i] * val + x) >> s;

camlibs/tp6801/library.c

@@ -151,9 +151,9 @@ get_file_func (CameraFilesystem *fs, const char *folder, const char *filename,
 	       GPContext *context)
 {
 	Camera *camera = data;
-	int idx, size;
+	int idx;
 #ifdef HAVE_LIBGD
-	int ret;
+	int ret, size;
 	gdImagePtr im;
 	void *gdpng;
 #endif