…(#194695) This relands the original commite3bd61890e(#191584). The original change was reverted in the following commits: 1)ec9d7d18bd(#194087) 2)c26ae41c87(#194695) This reland incorporates the following fixes: 1) Change LLVM_ENABLE_OPENCSD to default to OFF (opt-in). 2) Parse the OpenCSD version from ocsd_if_version.h and gate OpenCSD support on a minimum version of 1.5.4 to avoid compilation errors. 3) Refactor the test feature detection to use a configure-time LLVM_HAVE_OPENCSD variable instead of runtime checks in lit.local.cfg.