[PATCH] error_code for dynamically generated error messages

[Rui Ueyama]

The idea looks good to me.

================
Comment at: lib/Core/Error.cpp:182
@@ +181,3 @@
+    if (_messages.empty())
+      _messages.push_back("Success");
+    _messages.push_back(msg);
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What is this for?

================
Comment at: lib/Core/Error.cpp:190
@@ +189,3 @@
+  std::vector<std::string> _messages;
+  llvm::sys::SmartMutex<true> _mutex;
+};
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Why don't you use std::mutex and std::lock_guard?

http://reviews.llvm.org/D3881