clang -flto=thin -O2 file1.o file2.o -o a.out -glto-dwo-dir=./DWO_DIR -fuse-ld=lld 


/usr/bin/ld.lld: error: --plugin-opt: ld.lld: Unknown command line argument 'objcopy=/usr/bin/x86_64-pc-linux-gnu-objcopy'.  Try: '/usr/bin/ld.lld -help'
/usr/bin/ld.lld: error: --plugin-opt: ld.lld: Unknown command line argument 'dwo_dir=./yy'.  Try: '/usr/bin/ld.lld -help'
clang-7: error: linker command failed with exit code 1 (use -v to see invocation)