BE Put local SignedValueHandler into anonymous namespace to avoid sha…

…dowing

Reviewed By: Orvid

Differential Revision: D51939415

fbshipit-source-id: 63703ae18fb776481e26f113e99facc720a9d231

folly/Conv.cpp

@@ -463,6 +463,8 @@ template Expected<float, ConversionCode> str_to_floating<float>(
 template Expected<double, ConversionCode> str_to_floating<double>(
     StringPiece* src) noexcept;
 
+namespace {
+
 /**
  * This class takes care of additional processing needed for signed values,
  * like leading sign character and overflow checks.
@@ -530,6 +532,8 @@ class SignedValueHandler<T, false> {
   Expected<T, ConversionCode> finalize(T value) { return value; }
 };
 
+} // namespace
+
 /**
  * String represented as a pair of pointers to char to signed/unsigned
  * integrals. Assumes NO whitespace before or after, and also that the