[llvm] r175185 - Fix for bug 15246 -- out-of-bound error in the TableGen backend, CodeGenMapTable.cpp.

[Sean Silva]

I'm still doubting that this is fully correct. Just use standard
algorithms instead of hand-rolled ones. E.g. sort and then use
std::unique <http://en.cppreference.com/w/cpp/algorithm/unique>. This
also avoids any potential quadratic complexity issues. When sorting,
use one of the comparators in Record.h instead of pointer comparison
to avoid nondeterminism.

-- Sean Silva