[llvm-exegesis] Remove superfluous move.

/Users/buildslave/as-bldslv9_new/lld-x86_64-darwin13/llvm.src/tools/llvm-exegesis/lib/X86/Target.cpp:155:12: error: moving a local object in a return statement prevents copy elision [-Werror,-Wpessimizing-move]
    return std::move(Error);
           ^
/Users/buildslave/as-bldslv9_new/lld-x86_64-darwin13/llvm.src/tools/llvm-exegesis/lib/X86/Target.cpp:155:12: note: remove std::move call here
    return std::move(Error);
           ^~~~~~~~~~     ~

llvm-svn: 346333