Merge pull request #105 from haberman/dwarf-form

Fix for unused variable in opt build.
diff --git a/src/range_map.cc b/src/range_map.cc
index 8b13dbc..de8b91c 100644
--- a/src/range_map.cc
+++ b/src/range_map.cc
@@ -208,8 +208,7 @@
 
     uint64_t other = (otheraddr == kNoTranslation) ? kNoTranslation
                                                    : addr - base + otheraddr;
-    uint64_t this_size = this_end - addr;
-    assert(addr + this_size >= addr);
+    assert(this_end >= addr);
     auto iter = mappings_.emplace_hint(
         it, std::make_pair(addr, Entry(label, this_end - addr, other)));
     if (verbose_level > 2) {