Add a marker showing that we changed an upstream library.

system/lib/dlmalloc.c

@@ -4141,7 +4141,7 @@ static int sys_trim(mstate m, size_t pad) {
               sp->size >= extra &&
               !has_segment_link(m, sp)) { /* can't shrink if pinned */
             size_t newsize = sp->size - extra;
-            (void)newsize;
+            (void)newsize; // XXX EMSCRIPTEN
             /* Prefer mremap, fall back to munmap */
             if ((CALL_MREMAP(sp->base, sp->size, newsize, 0) != MFAIL) ||
                 (CALL_MUNMAP(sp->base + newsize, extra) == 0)) {