Work around weird behavior in GCC 4.8 where it thinks this destructor's…

Work around weird behavior in GCC 4.8 where it thinks this destructor's declaration and definition hase mismatching noexcept specs even though neither one has a noexcept spec at all.

c++/src/capnp/compiler/lexer.c++

@@ -269,7 +269,5 @@ Lexer::Lexer(Orphanage orphanageParam, const ErrorReporter& errorReporterParam)
   parsers.emptySpace = commentsAndWhitespace;
 }
 
-Lexer::~Lexer() {}
-
 }  // namespace compiler
 }  // namespace capnp

c++/src/capnp/compiler/lexer.h

@@ -53,8 +53,6 @@ public:
   // `orphanage` is used to allocate Cap'n Proto message objects in the result.  `inputStart` is
   // a pointer to the beginning of the input, used to compute byte offsets.
 
-  ~Lexer();
-
   class ParserInput: public kj::parse::IteratorInput<char, const char*> {
     // Like IteratorInput<char, const char*> except that positions are measured as byte offsets
     // rather than pointers.