remove redefinition of typedefs

We had this in a couple of places:

	typedef struct _A A;
	typedef struct _A A;

Some old gccs (eg. centos6) throw errors for this.

See https://github.com/libvips/libvips/issues/1774

ChangeLog

@@ -1,5 +1,6 @@
 9/8/20 started 8.10.1
 - fix markdown -> xml conversion in doc generation
+- remove typedef redefinitions to please old gccs
 
 24/1/20 started 8.10.0
 - more conformat IIIF output from dzsave [regisrob]

libvips/foreign/ppmsave.c

@@ -62,7 +62,7 @@ typedef struct _VipsForeignSavePpm VipsForeignSavePpm;
 
 typedef int (*VipsSavePpmFn)( VipsForeignSavePpm *, VipsImage *, VipsPel * );
 
-typedef struct _VipsForeignSavePpm {
+struct _VipsForeignSavePpm {
 	VipsForeignSave parent_object;
 
 	VipsTarget *target;
@@ -74,7 +74,7 @@ typedef struct _VipsForeignSavePpm {
 	/* Deprecated.
 	 */
 	gboolean squash;
-} VipsForeignSavePpm;
+};
 
 typedef VipsForeignSaveClass VipsForeignSavePpmClass;
 

libvips/include/vips/image.h

@@ -133,8 +133,8 @@ typedef enum {
 	VIPS_ACCESS_LAST
 } VipsAccess;
 
-typedef void *(*VipsStartFn)( struct _VipsImage *out, void *a, void *b );
+typedef void *(*VipsStartFn)( VipsImage *out, void *a, void *b );
-typedef int (*VipsGenerateFn)( struct _VipsRegion *out, 
+typedef int (*VipsGenerateFn)( VipsRegion *out, 
 	void *seq, void *a, void *b, gboolean *stop );
 typedef int (*VipsStopFn)( void *seq, void *a, void *b );
 
@@ -143,7 +143,7 @@ typedef int (*VipsStopFn)( void *seq, void *a, void *b );
  */
 typedef struct _VipsProgress {
 	/*< private >*/
-	struct _VipsImage *im;	/* Image we are part of */
+	VipsImage *im;		/* Image we are part of */
 
 	/*< public >*/
 	int run;		/* Time we have been running */
@@ -169,7 +169,9 @@ typedef struct _VipsProgress {
 	(G_TYPE_INSTANCE_GET_CLASS( (obj), \
 	VIPS_TYPE_IMAGE, VipsImageClass ))
 
-typedef struct _VipsImage {
+/* Matching typedef in basic.h.
+ */
+struct _VipsImage {
 	VipsObject parent_instance;
 
 	/*< private >*/
@@ -281,7 +283,7 @@ typedef struct _VipsImage {
 
 	/* The VipsImage (if any) we should signal eval progress on.
 	 */
-	struct _VipsImage *progress_signal;
+	VipsImage *progress_signal;
 
 	/* Record the file length here. We use this to stop ourselves mapping
 	 * things beyond the end of the file in the case that the file has
@@ -309,7 +311,7 @@ typedef struct _VipsImage {
 	 */
 	gboolean delete_on_close;
 	char *delete_on_close_filename;
-} VipsImage;
+};
 
 typedef struct _VipsImageClass {
 	VipsObjectClass parent_class;
@@ -519,7 +521,7 @@ void vips_value_set_array_image( GValue *value, int n );
 /* Defined in reorder.c, but really a function on image.
  */
 int vips_reorder_prepare_many( VipsImage *image, 
-	struct _VipsRegion **regions, VipsRect *r );
+	VipsRegion **regions, VipsRect *r );
 void vips_reorder_margin_hint( VipsImage *image, int margin );
 
 #ifdef __cplusplus

libvips/include/vips/region.h

@@ -77,8 +77,10 @@ typedef enum {
 } VipsRegionShrink;
 
 /* Sub-area of image.
+ *
+ * Matching typedef in basic.h.
  */
-typedef struct _VipsRegion {
+struct _VipsRegion {
 	VipsObject parent_object;
 
 	/*< public >*/
@@ -112,7 +114,7 @@ typedef struct _VipsRegion {
 	 * dropped.
 	 */
 	gboolean invalid;	
-} VipsRegion;
+};
 
 typedef struct _VipsRegionClass {
 	VipsObjectClass parent_class;