Use platform independent type for TupleTableSlot->tts_off.

Previously tts_off was, for unknown reasons, of type long. For one
that's unnecessary as tuples are restricted in length, for another
long would be a bad choice of type even if that weren't the case, as
it's not reliably wider than an int. Also HeapTupleHeader->t_len is a
uint32.

This is split off from a larger patch implementing JITed tuple
deforming. Seems like an independent improvement, as tiny as it is.

Author: Andres Freund

src/backend/access/common/heaptuple.c

@@ -942,7 +942,7 @@ heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
 	int			natts;			/* number of atts to extract */
 	int			attnum;
 	char	   *tp;				/* ptr to tuple data */
-	long		off;			/* offset in tuple data */
+	uint32		off;			/* offset in tuple data */
 	bits8	   *bp = tup->t_bits;	/* ptr to null bitmap in tuple */
 	bool		slow = false;	/* can we use/set attcacheoff? */
 
@@ -1043,7 +1043,7 @@ slot_deform_tuple(TupleTableSlot *slot, int natts)
 	bool		hasnulls = HeapTupleHasNulls(tuple);
 	int			attnum;
 	char	   *tp;				/* ptr to tuple data */
-	long		off;			/* offset in tuple data */
+	uint32		off;			/* offset in tuple data */
 	bits8	   *bp = tup->t_bits;	/* ptr to null bitmap in tuple */
 	bool		slow;			/* can we use/set attcacheoff? */
 

src/include/executor/tuptable.h

@@ -126,7 +126,7 @@ typedef struct TupleTableSlot
 	bool	   *tts_isnull;		/* current per-attribute isnull flags */
 	MinimalTuple tts_mintuple;	/* minimal tuple, or NULL if none */
 	HeapTupleData tts_minhdr;	/* workspace for minimal-tuple-only case */
-	long		tts_off;		/* saved state for slot_deform_tuple */
+	uint32		tts_off;		/* saved state for slot_deform_tuple */
 	bool		tts_fixedTupleDescriptor; /* descriptor can't be changed */
 } TupleTableSlot;