[DX] Add analysis and printer for shader flags

[DX] Add analysis and printer for shader flags

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