Don't declare caught exceptions when not actually used

Summary: There are a couple of places where the caught exception was being given a name that was never used, generating a warning under MSVC.

Reviewed By: simpkins

Differential Revision: D5260131

fbshipit-source-id: f82c6bd1266f6a4c916594ec3ac94edc9a2e48fe

folly/experimental/logging/LogLevel.cpp

@@ -76,7 +76,7 @@ LogLevel stringToLogLevel(StringPiece name) {
   try {
     auto level = folly::to<uint32_t>(lowerName);
     return static_cast<LogLevel>(level);
-  } catch (const std::exception& ex) {
+  } catch (const std::exception&) {
     throw std::range_error("invalid logger name " + name.str());
   }
 }

folly/experimental/logging/LogStream.cpp

@@ -38,7 +38,7 @@ LogStreamBuffer::int_type LogStreamBuffer::overflow(int_type ch) {
       setp((&str_.front()) + currentSize + 1, (&str_.front()) + newSize);
       return ch;
     }
-  } catch (const std::exception& ex) {
+  } catch (const std::exception&) {
     // Return EOF to indicate that the operation failed.
     // In general the only exception we really expect to see here is
     // std::bad_alloc() from the str_.resize() call.