Fixes #225 ("variable set but not used in dlmalloc_ext_2_8_6.c")

doc/container.qbk

@@ -1414,6 +1414,7 @@ use [*Boost.Container]? There are several reasons for that:
 * Disabled forceinline for Clang due to code bloat issues, see [@https://lists.boost.org/boost-users/2023/04/91445.php Boost mailing list report]
 
 * Fixed bugs/issues:
+   * [@https://github.com/boostorg/container/issues/225 GitHub #225: ['"variable set but not used in dlmalloc_ext_2_8_6.c"]].
    * [@https://github.com/boostorg/container/issues/242 GitHub #242: ['"Issue with string::rfind"]].
 
 [endsect]

src/dlmalloc_2_8_6.c

@@ -4013,6 +4013,7 @@ static void add_segment(mstate m, char* tbase, size_t tsize, flag_t mmapped) {
       break;
   }
   assert(nfences >= 2);
+  (void) nfences; //Added by iG to silence warning about unused nfences
 
   /* Insert the rest of old top into a bin as an ordinary free chunk */
   if (csp != old_top) {

src/dlmalloc_ext_2_8_6.c

@@ -1224,14 +1224,12 @@ size_t boost_cont_allocated_memory()
       if (is_initialized(m)) {
       size_t nfree = SIZE_T_ONE; /* top always free */
       size_t mfree = m->topsize + TOP_FOOT_SIZE;
-      size_t sum = mfree;
       msegmentptr s = &m->seg;
       while (s != 0) {
          mchunkptr q = align_as_chunk(s->base);
          while (segment_holds(s, q) &&
                q != m->top && q->head != FENCEPOST_HEAD) {
             size_t sz = chunksize(q);
-            sum += sz;
             if (!is_inuse(q)) {
             mfree += sz;
             ++nfree;