[NFC][SYCL][SYCLLowerIR] Add cl::opt SpecConstantMode for LIT testing#15821

steffenlarsen merged 2 commits intointel:syclintel/llvm:syclfrom

wenju-he:SpecConstantsPass-cl-opt-SpecConstantModewenju-he/llvm:SpecConstantsPass-cl-opt-SpecConstantModeCopy head branch name to clipboard