- added `FindZSTD.cmake` - added a CMake option `LLVM_ENABLE_ZSTD` with behavior mirroring that of `LLVM_ENABLE_ZLIB` - likewise added have_zstd to compiler-rt/test/lit.common.cfg.py, clang-tools-extra/clangd/test/lit.cfg.py, and several lit.site.cfg.py.in files mirroring have_zlib behavior - add zstd compression namespace

- add `FindZSTD.cmake` - add zstd to `llvm::compression` namespace - add a CMake option `LLVM_ENABLE_ZSTD` with behavior mirroring that of `LLVM_ENABLE_ZLIB` - add tests for zstd to `llvm/unittests/Support/CompressionTest.cpp`

- added `FindZSTD.cmake` - added a CMake option `LLVM_ENABLE_ZSTD` with behavior mirroring that of `LLVM_ENABLE_ZLIB` zstd to `llvm::compression` namespace - likewise added have_zstd to compiler-rt/test/lit.common.cfg.py, clang-tools-extra/clangd/test/lit.cfg.py, and several lit.site.cfg.py.in files mirroring have_zlib behavioradd a CMake option `LLVM_ENABLE_ZSTD` with behavior mirroring that of `LLVM_ENABLE_ZLIB` - add tests for zstd cto `llvm/unittests/Support/Compression namespaceTest.cpp`