Avoid compiler warning for keepersize assert only variable

Reviewed-by: NPaul Guo <guopa@vmware.com>

src/backend/utils/mmgr/aset.c

@@ -690,7 +690,7 @@ AllocSetReset(MemoryContext context)
 {
 	AllocSet	set = (AllocSet) context;
 	AllocBlock	block;
-	Size		keepersize = set->keeper->endptr - ((char *) set);
+	Size		keepersize PG_USED_FOR_ASSERTS_ONLY = set->keeper->endptr - ((char *) set);
 
 	AssertArg(AllocSetIsValid(set));
 
@@ -764,7 +764,7 @@ AllocSetDelete(MemoryContext context, MemoryContext parent)
 {
 	AllocSet	set = (AllocSet) context;
 	AllocBlock	block = set->blocks;
-	Size		keepersize = set->keeper->endptr - ((char *) set);
+	Size		keepersize PG_USED_FOR_ASSERTS_ONLY = set->keeper->endptr - ((char *) set);
 
 	AssertArg(AllocSetIsValid(set));