Add two hidden options for emitting SPIR-V binary via LLC. The options are only meant for testing and development.
´--spirv-use-llc´ invokes in-tree llc. Not usable at the moment until the SPIR-V backend lands on LLVM.
´--spirv-use-llc=<path-to-llc>´ invokes llc tool given as path. Meant for trying out out-of-tree SPIR-V backend.
The HIPSPV tool chain is the only one responding to these options.