[clang] [OFFLOAD] Add headers to support complex math for spirv (PR #179846)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 commented:

Are these substantially different from the ones we already have? Also in theory the build I have of `compiler-rt` is a better solution for this. Only reason I haven't told people to move to that is because building with compiler-rt enabled is a chore because of CMake constantly re-running 

https://github.com/llvm/llvm-project/pull/179846