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

src/conversions-inl.h

Index: src/conversions-inl.h
diff --git a/src/conversions-inl.h b/src/conversions-inl.h
index f1f526ffc0260c18c9cda5a14b8f6892aa3aaf1e..b828638568aa8e687773c52f51472ac20b7f56e5 100644
--- a/src/conversions-inl.h
+++ b/src/conversions-inl.h
@@ -454,7 +454,6 @@ static double InternalStringToDouble(UnicodeCache* unicode_cache,
   int significant_digits = 0;
   int insignificant_digits = 0;
   bool nonzero_digit_dropped = false;
-  bool fractional_part = false;
 
   bool negative = false;
 
@@ -557,10 +556,8 @@ static double InternalStringToDouble(UnicodeCache* unicode_cache,
       }
     }
 
-    // We don't emit a '.', but adjust the exponent instead.
-    fractional_part = true;
-
-    // There is a fractional part.
+    // There is a fractional part.  We don't emit a '.', but adjust the exponent
+    // instead.
     while (*current >= '0' && *current <= '9') {
       if (significant_digits < kMaxSignificantDigits) {
         ASSERT(buffer_pos < kBufferSize);