[regexp] Work around gcc bug triggering -Werror=strict-overflow

BUG=v8:5526

Review-Url: https://codereview.chromium.org/2422173003
Cr-Commit-Position: refs/heads/master@{#40368}

src/runtime/runtime-regexp.cc

@@ -1338,8 +1338,8 @@ MaybeHandle<String> StringReplaceNonGlobalRegExpWithFunction(
     }
   }
 
-  argv[m] = handle(Smi::FromInt(index), isolate);
-  argv[m + 1] = subject;
+  argv[argc - 2] = handle(Smi::FromInt(index), isolate);
+  argv[argc - 1] = subject;
 
   Handle<Object> replacement_obj;
   ASSIGN_RETURN_ON_EXCEPTION(

src/vector.h

@@ -51,7 +51,8 @@ class Vector {
 
   // Access individual vector elements - checks bounds in debug mode.
   T& operator[](int index) const {
-    DCHECK(0 <= index && index < length_);
+    DCHECK_LE(0, index);
+    DCHECK_LT(index, length_);
     return start_[index];
   }