fix some compiler warnings

from the msvc patch

ChangeLog

@@ -23,6 +23,7 @@
 - add vips_transpose3d() -- swap major dimensions in a volumetric image
 - remove vips7 stuff from default API ... you must now #include it explicitly
 - added vips_argument_get_id() to fix derived classes on win32 [angelmixu]
+- fix compile with MSVC 2017 [angelmixu]
 
 12/3/18 started 8.6.4
 - better fitting of fonts with overhanging edges [Adrià]

libvips/foreign/tiff2vips.c

@@ -1843,7 +1843,7 @@ rtiff_stripwise_generate( VipsRegion *or,
 
 			/* Do any repacking to generate pixels in vips layout.
 			 */
-			p = (char*)(rtiff->contig_buf) + 
+			p = (VipsPel *) rtiff->contig_buf + 
 				(hit.top - strip.top) * scanline_size;
 			q = VIPS_REGION_ADDR( or, 0, r->top + y );
 			for( z = 0; z < hit.height; z++ ) { 

libvips/foreign/vipspng.c

@@ -700,7 +700,7 @@ vips_png_read_buffer( png_structp pPng, png_bytep data, png_size_t length )
 	if( read->read_pos + length > read->length )
 		png_error( pPng, "not enough data in buffer" );
 
-	memcpy( data, (const char*)(read->buffer) + read->read_pos, length );
+	memcpy( data, (VipsPel *) read->buffer + read->read_pos, length );
 	read->read_pos += length;
 }
 

libvips/include/vips/type.h

@@ -100,7 +100,8 @@ void *vips_area_get_data( VipsArea *area,
 #ifdef VIPS_DEBUG
 #define VIPS_ARRAY_ADDR( X, I ) \
 	(((I) >= 0 && (I) < VIPS_AREA( X )->n) ? \
-	 ((char*)(VIPS_AREA( X )->data) + VIPS_AREA( X )->sizeof_type * (I)) : \
+	 (void *) ((VipsPel *) VIPS_AREA( X )->data + \
+	  	VIPS_AREA( X )->sizeof_type * (I)) : \
 	 (fprintf( stderr, \
 		"VIPS_ARRAY_ADDR: index out of bounds, " \
 		"file \"%s\", line %d\n" \
@@ -109,7 +110,8 @@ void *vips_area_get_data( VipsArea *area,
 		(I), VIPS_AREA( X )->n ), NULL ))
 #else /*!VIPS_DEBUG*/
 #define VIPS_ARRAY_ADDR( X, I ) \
-	((char*)(VIPS_AREA( X )->data) + VIPS_AREA( X )->sizeof_type * (I))
+	((void *) \
+	 ((VipsPel *) VIPS_AREA( X )->data + VIPS_AREA( X )->sizeof_type * (I)))
 #endif /*VIPS_DEBUG*/
 
 /**

libvips/iofuncs/image.c

@@ -3269,7 +3269,8 @@ vips_image_wio_input( VipsImage *image )
 		 */
 		if( vips_mapfile( image ) ) 
 			return( -1 );
-		image->data = ((char*)image->baseaddr) + image->sizeof_header;
+		image->data = (VipsPel *) image->baseaddr + 
+			image->sizeof_header;
 		image->dtype = VIPS_IMAGE_MMAPIN;
 
 		break;