Changed Op.compare_upper => Op.compare_lower to fix flang build.
Added workaround for APFloat interface change.

I will eventually add something like this to APFloat in llvm. But for hacking
purposes I am just going to leave the function here for now.
Added Flang specific tablegen.

This tablegen backend was created by slicing and dicing the clang tablegen.
Fixed incompatibility in DeclSpec.cpp with new flang tablegen.