This is a separate tool so we can use all of LLVM without worrying about
creating a dependency from the demangler on LLVM's libsupport.
I am going to use it to fix cmpcodesize for the new mangling by eliminating
cmpcodesize's usage of regex to classify symbols. Instead, we can just read in
the yaml version of the symbol trees for each demangled node and process that
instead.
rdar://41146023
