This adds infrastructural pieces for an analysis to compute the DXIL
shader flags. In this state the analysis can compute two fairly
straightforward feature flags for use of double-precision floating
point values and the DX 11.1 extended double support.
This patch does conflict with D135190, conflicts will be resolved prior
to merging.
Reviewed By: python3kgae
Differential Revision: https://reviews.llvm.org/D135393
# Conflicts:
# llvm/lib/Target/DirectX/CMakeLists.txt
# llvm/lib/Target/DirectX/DirectXTargetMachine.cpp
