Fix GCC 4.7 warnings.

src/string-search.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 351 matching lines @@
   int* shift_table = good_suffix_shift_table();
   int* suffix_table = this->suffix_table();
 
   // Initialize table.
   for (int i = start; i < pattern_length; i++) {
     shift_table[i] = length;
   }
   shift_table[pattern_length] = 1;
   suffix_table[pattern_length] = pattern_length + 1;
 
+  if (pattern_length <= start) {
+    return;
+  }
+
   // Find suffixes.
   PatternChar last_char = pattern[pattern_length - 1];
   int suffix = pattern_length + 1;
   {
     int i = pattern_length;
     while (i > start) {
       PatternChar c = pattern[i - 1];
       while (suffix <= pattern_length && c != pattern[suffix - 1]) {
         if (shift_table[suffix] == length) {
           shift_table[suffix] = suffix - i;
@@ skipping 177 matching lines @@
                  Vector<const SubjectChar> subject,
                  Vector<const PatternChar> pattern,
                  int start_index) {
   StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
   return search.Search(subject, start_index);
 }
 
 }}  // namespace v8::internal
 
 #endif  // V8_STRING_SEARCH_H_