This makes lld-link's output a bit more concise. Since most developers can't read mangled names, this should make the output a bit easier to understand as well. It also makes lld-link's output consistent with ld.lld's output.
(link.exe prints both demangled and mangled names; lld-link used to match link.exe output but now no longer does.)
For people working on toolchains, add a /demangle:no flag that makes lld-link print the mangled name instead of the demangled name. (If desired, people could pipe that through demumble -b to get the old behavior of both demangled and mangled output.)