Suppress more variable-set-but-not-used warnings from clang 15.

Mop up assorted set-but-not-used warnings in the back branches.
This includes back-patching relevant fixes from commit 152c9f7b8
the rest of the way, but there are also several cases that did not
appear in HEAD.  Some of those we'd fixed in a retail way but not
back-patched, and others I think just got rewritten out of existence
during nearby refactoring.

While here, also back-patch b1980f6d0 (PL/Tcl: Fix compiler warnings
with Tcl 8.6) into 9.2, so that that branch compiles warning-free
with modern Tcl.

Per project policy, this is a candidate for back-patching into
out-of-support branches: it suppresses annoying compiler warnings
but changes no behavior.  Hence, back-patch all the way to 9.2.

Discussion: https://postgr.es/m/514615.1663615243@sss.pgh.pa.us

contrib/hstore/crc32.c

@@ -95,12 +95,10 @@ crc32_sz(char *buf, int size)
 {
 	unsigned int crc = ~((unsigned int) 0);
 	char	   *p;
-	int			len,
-				nr;
+	int			nr;
 
-	len = 0;
 	nr = size;
-	for (len += nr, p = buf; nr--; ++p)
+	for (p = buf; nr--; ++p)
 		_CRC32_(crc, *p);
 	return ~crc;
 }

contrib/ltree/crc32.c

@@ -103,12 +103,10 @@ ltree_crc32_sz(char *buf, int size)
 {
 	unsigned int crc = ~((unsigned int) 0);
 	char	   *p;
-	int			len,
-				nr;
+	int			nr;
 
-	len = 0;
 	nr = size;
-	for (len += nr, p = buf; nr--; ++p)
+	for (p = buf; nr--; ++p)
 		_CRC32_(crc, TOLOWER((unsigned int) *p));
 	return ~crc;
 }

src/backend/access/transam/xlog.c

@@ -2159,7 +2159,9 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 	XLogRecPtr	NewPageEndPtr = InvalidXLogRecPtr;
 	XLogRecPtr	NewPageBeginPtr;
 	XLogPageHeader NewPage;
+#ifdef WAL_DEBUG
 	int			npages = 0;
+#endif
 
 	LWLockAcquire(WALBufMappingLock, LW_EXCLUSIVE);
 
@@ -2306,7 +2308,9 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 
 		XLogCtl->InitializedUpTo = NewPageEndPtr;
 
+#ifdef WAL_DEBUG
 		npages++;
+#endif
 	}
 	LWLockRelease(WALBufMappingLock);
 

src/backend/optimizer/util/var.c

@@ -651,16 +651,13 @@ flatten_join_alias_vars_mutator(Node *node,
 			RowExpr    *rowexpr;
 			List	   *fields = NIL;
 			List	   *colnames = NIL;
-			AttrNumber	attnum;
 			ListCell   *lv;
 			ListCell   *ln;
 
-			attnum = 0;
 			Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
 			forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
 			{
 				newvar = (Node *) lfirst(lv);
-				attnum++;
 				/* Ignore dropped columns */
 				if (newvar == NULL)
 					continue;

src/backend/parser/gram.y

@@ -690,6 +690,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 stmtblock:	stmtmulti
 			{
 				pg_yyget_extra(yyscanner)->parsetree = $1;
+				(void) yynerrs;		/* suppress compiler warning */
 			}
 		;
 

src/backend/utils/adt/array_typanalyze.c

@@ -216,7 +216,6 @@ compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
 {
 	ArrayAnalyzeExtraData *extra_data;
 	int			num_mcelem;
-	int			null_cnt = 0;
 	int			null_elem_cnt = 0;
 	int			analyzed_rows = 0;
 
@@ -321,8 +320,7 @@ compute_array_stats(VacAttrStats *stats, AnalyzeAttrFetchFunc fetchfunc,
 		value = fetchfunc(stats, array_no, &isnull);
 		if (isnull)
 		{
-			/* array is null, just count that */
-			null_cnt++;
+			/* ignore arrays that are null overall */
 			continue;
 		}
 

src/backend/utils/adt/varlena.c

@@ -3403,7 +3403,6 @@ text_to_array_internal(PG_FUNCTION_ARGS)
 		 * to search for occurrences of fldsep.
 		 */
 		TextPositionState state;
-		int			fldnum;
 		int			start_posn;
 		int			end_posn;
 		int			chunk_len;
@@ -3443,7 +3442,7 @@ text_to_array_internal(PG_FUNCTION_ARGS)
 		/* start_ptr points to the start_posn'th character of inputstring */
 		start_ptr = VARDATA_ANY(inputstring);
 
-		for (fldnum = 1;; fldnum++)		/* field number is 1 based */
+		for (;;)
 		{
 			CHECK_FOR_INTERRUPTS();