[HLSL]Add -O and -Od option for dxc mode.

Two new dxc mode options -O and -Od are added for dxc mode.
-O is just alias of existing cc1 -O option.
-Od will be lowered into -O0 and -dxc-opt-disable.

-dxc-opt-disable is cc1 option added to for build ShaderFlags.

Reviewed By: beanz

Differential Revision: https://reviews.llvm.org/D128845