[compiler-rt] [compiler-rt] Partially enable building compiler-rt unit tests for spirv64 target (PR #215717)

[via llvm-commits]

jinge90 wrote:

Hi, @sarnex and @srividya-sundaram 
This PR is the 1st one to fix the some build errors you encountered when building compiler-rt tests for spirv64 target, could you help review it? More patches will be submitted to fix left errors.
Thanks very much.

https://github.com/llvm/llvm-project/pull/215717