Mark a few functions noexcept.

This reduces the difference between std::error_code and llvm::error_code.

llvm-svn: 210591
diff --git a/llvm/tools/llvm-readobj/Error.cpp b/llvm/tools/llvm-readobj/Error.cpp
index 75c392e..424dfbe 100644
--- a/llvm/tools/llvm-readobj/Error.cpp
+++ b/llvm/tools/llvm-readobj/Error.cpp
@@ -19,9 +19,9 @@
 namespace {
 class _readobj_error_category : public error_category {
 public:
-  const char* name() const override;
+  const char* name() const LLVM_NOEXCEPT override;
   std::string message(int ev) const override;
-  error_condition default_error_condition(int ev) const override;
+  error_condition default_error_condition(int ev) const LLVM_NOEXCEPT override;
 };
 } // namespace