[NFC][clang-sycl-linker] Rename runSPIRVCodeGen to runCodeGen. (#179372)
`runSPIRVCodeGen` function doesn't use SPIR-V backend explicitly. The
backend is chosen based on `-triple` option value. Technically
`clang-sycl-linker` tool can emit PTX or a binary format based on the
triple value.
Fixed comments.