Make NUM_TOCHAR_prepare and NUM_TOCHAR_finish macros declare "len".

Remove the variable from the enclosing scopes so that nothing can be
relying on it.  The net result of this refactoring is that we get rid
of a few unnecessary strlen() calls.

Original patch from Greg Jaskiewicz, substantially expanded by me.

src/backend/utils/adt/formatting.c

@@ -4877,7 +4877,7 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout, char *number,
  */
 #define NUM_TOCHAR_prepare \
 do { \
-	len = VARSIZE_ANY_EXHDR(fmt); \
+	int len = VARSIZE_ANY_EXHDR(fmt); \
 	if (len <= 0 || len >= (INT_MAX-VARHDRSZ)/NUM_MAX_ITEM_SIZ)		\
 		PG_RETURN_TEXT_P(cstring_to_text("")); \
 	result	= (text *) palloc0((len * NUM_MAX_ITEM_SIZ) + 1 + VARHDRSZ);	\
@@ -4890,6 +4890,8 @@ do { \
  */
 #define NUM_TOCHAR_finish \
 do { \
+	int		len; \
+									\
 	NUM_processor(format, &Num, VARDATA(result), numstr, plen, sign, true, PG_GET_COLLATION()); \
 									\
 	if (shouldFree)					\
@@ -4961,8 +4963,7 @@ numeric_to_char(PG_FUNCTION_ARGS)
 	FormatNode *format;
 	text	   *result;
 	bool		shouldFree;
-	int			len = 0,
-				plen = 0,
+	int			plen = 0,
 				sign = 0;
 	char	   *numstr,
 			   *orgnum,
@@ -5008,16 +5009,15 @@ numeric_to_char(PG_FUNCTION_ARGS)
 			numstr = (char *) palloc(strlen(orgnum) + 2);
 			*numstr = ' ';
 			strcpy(numstr + 1, orgnum);
-			len = strlen(numstr);
 		}
 		else
 		{
 			numstr = orgnum;
-			len = strlen(orgnum);
 		}
 	}
 	else
 	{
+		int			len;
 		Numeric		val = value;
 
 		if (IS_MULTI(&Num))
@@ -5084,8 +5084,7 @@ int4_to_char(PG_FUNCTION_ARGS)
 	FormatNode *format;
 	text	   *result;
 	bool		shouldFree;
-	int			len = 0,
-				plen = 0,
+	int			plen = 0,
 				sign = 0;
 	char	   *numstr,
 			   *orgnum;
@@ -5111,11 +5110,12 @@ int4_to_char(PG_FUNCTION_ARGS)
 		if (*orgnum == '+')
 			*orgnum = ' ';
 
-		len = strlen(orgnum);
 		numstr = orgnum;
 	}
 	else
 	{
+		int			len;
+
 		if (IS_MULTI(&Num))
 		{
 			orgnum = DatumGetCString(DirectFunctionCall1(int4out,
@@ -5175,8 +5175,7 @@ int8_to_char(PG_FUNCTION_ARGS)
 	FormatNode *format;
 	text	   *result;
 	bool		shouldFree;
-	int			len = 0,
-				plen = 0,
+	int			plen = 0,
 				sign = 0;
 	char	   *numstr,
 			   *orgnum;
@@ -5211,16 +5210,16 @@ int8_to_char(PG_FUNCTION_ARGS)
 			numstr = (char *) palloc(strlen(orgnum) + 2);
 			*numstr = ' ';
 			strcpy(numstr + 1, orgnum);
-			len = strlen(numstr);
 		}
 		else
 		{
 			numstr = orgnum;
-			len = strlen(orgnum);
 		}
 	}
 	else
 	{
+		int			len;
+
 		if (IS_MULTI(&Num))
 		{
 			double		multi = pow((double) 10, (double) Num.multi);
@@ -5282,8 +5281,7 @@ float4_to_char(PG_FUNCTION_ARGS)
 	FormatNode *format;
 	text	   *result;
 	bool		shouldFree;
-	int			len = 0,
-				plen = 0,
+	int			plen = 0,
 				sign = 0;
 	char	   *numstr,
 			   *orgnum,
@@ -5317,13 +5315,13 @@ float4_to_char(PG_FUNCTION_ARGS)
 			if (*orgnum == '+')
 				*orgnum = ' ';
 
-			len = strlen(orgnum);
 			numstr = orgnum;
 		}
 	}
 	else
 	{
 		float4		val = value;
+		int			len;
 
 		if (IS_MULTI(&Num))
 		{
@@ -5386,8 +5384,7 @@ float8_to_char(PG_FUNCTION_ARGS)
 	FormatNode *format;
 	text	   *result;
 	bool		shouldFree;
-	int			len = 0,
-				plen = 0,
+	int			plen = 0,
 				sign = 0;
 	char	   *numstr,
 			   *orgnum,
@@ -5421,13 +5418,13 @@ float8_to_char(PG_FUNCTION_ARGS)
 			if (*orgnum == '+')
 				*orgnum = ' ';
 
-			len = strlen(orgnum);
 			numstr = orgnum;
 		}
 	}
 	else
 	{
 		float8		val = value;
+		int			len;
 
 		if (IS_MULTI(&Num))
 		{