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

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fineg74 wrote:

Refactored the change so it reuses existing implementation to minimize the changes. While compiler-rt may be a better solution there is a test that uses this functionality so we might need to support it until everything is migrated to compiler-rt

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