fix -Wunused-but-set-variable for gcc-4.6 on x64

src/x64/regexp-macro-assembler-x64.cc

Index: src/x64/regexp-macro-assembler-x64.cc
diff --git a/src/x64/regexp-macro-assembler-x64.cc b/src/x64/regexp-macro-assembler-x64.cc
index 2ea17f0e96848ebb1dbc1f65af0398bcaf3fcf66..395466e7774a82489c216aec0c64c68fea37d412 100644
--- a/src/x64/regexp-macro-assembler-x64.cc
+++ b/src/x64/regexp-macro-assembler-x64.cc
@@ -661,7 +661,6 @@ bool RegExpMacroAssemblerX64::CheckSpecialCharacterClass(uc16 type,
     }
     __ movq(rbx, ExternalReference::re_word_character_map());
     ASSERT_EQ(0, word_character_map[0]);  // Character '\0' is not a word char.
-    ExternalReference word_map = ExternalReference::re_word_character_map();
     __ testb(Operand(rbx, current_character(), times_1, 0),
              current_character());
     BranchOrBacktrack(zero, on_no_match);
@@ -676,7 +675,6 @@ bool RegExpMacroAssemblerX64::CheckSpecialCharacterClass(uc16 type,
     }
     __ movq(rbx, ExternalReference::re_word_character_map());
     ASSERT_EQ(0, word_character_map[0]);  // Character '\0' is not a word char.
-    ExternalReference word_map = ExternalReference::re_word_character_map();
     __ testb(Operand(rbx, current_character(), times_1, 0),
              current_character());
     BranchOrBacktrack(not_zero, on_no_match);