Compile fix for Apple's handicapped clang.

libdevcore/Exceptions.h

@@ -31,7 +31,7 @@
 namespace dev
 {
 // base class for all exceptions
-struct Exception: virtual std::exception, virtual boost::exception {};
+struct Exception: virtual std::exception, virtual boost::exception { mutable std::string m_message; };
 
 struct BadHexCharacter: virtual Exception {};
 struct RLPException: virtual Exception {};

libethcore/Exceptions.cpp

@@ -27,11 +27,14 @@ using namespace std;
 using namespace dev;
 using namespace dev::eth;
 
-#if _MSC_VER
-#define thread_local __declspec( thread )
-#endif
-
+#if ALL_COMPILERS_ARE_CPP11
 #define ETH_RETURN_STRING(S) thread_local static string s_what; s_what = S; return s_what.c_str();
+#elsif USE_BOOST_TLS
+static boost::thread_specific_ptr<string> g_exceptionMessage;
+#define ETH_RETURN_STRING(S) if (!g_exceptionMessage.get()); g_exceptionMessage.reset(new string); *g_exceptionMessage.get() = S; return g_exceptionMessage.get()->c_str();
+#else
+#define ETH_RETURN_STRING(S) m_message = S; return m_message.c_str();
+#endif
 
 const char* InvalidBlockFormat::what() const noexcept { ETH_RETURN_STRING("Invalid block format: Bad field " + toString(m_f) + " (" + toHex(m_d) + ")"); }
 const char* UncleInChain::what() const noexcept { ETH_RETURN_STRING("Uncle in block already mentioned: Uncles " + toString(m_uncles) + " (" + m_block.abridged() + ")"); }