[llvm] [llvm-readobj] enable demangle option for the xcoff object file (PR #78455)

[via llvm-commits]

stephenpeckham wrote:

This looks okay.  Is it worth eliminating some of the calls to demangle()?  For example, you could pass the demangled name to printLoaderSectionRelocationEntry(). Or call demangle() once in printRelocation().  But for a simple utility program, it may not be worth the effort to make this kind of change.

https://github.com/llvm/llvm-project/pull/78455