Add FIXMEs to all derived classes of std::error_category.

This helps make clear that we're moving away from std::error_code.

Differential Revision: http://reviews.llvm.org/D20592

llvm-svn: 270604
diff --git a/llvm/lib/Support/Error.cpp b/llvm/lib/Support/Error.cpp
index 9007e69..564b763 100644
--- a/llvm/lib/Support/Error.cpp
+++ b/llvm/lib/Support/Error.cpp
@@ -19,6 +19,9 @@
     MultipleErrors
   };
 
+  // FIXME: This class is only here to support the transition to llvm::Error. It
+  // will be removed once this transition is complete. Clients should prefer to
+  // deal with the Error value directly, rather than converting to error_code.
   class ErrorErrorCategory : public std::error_category {
   public:
     const char *name() const LLVM_NOEXCEPT override { return "Error"; }