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

[James Henderson via llvm-commits]

================
@@ -94,6 +99,11 @@ file formats.
 
  Display the needed libraries.
 
+.. option:: --no-demangle
+
+ Not demangle symbol names in the output; the option is only for ELF and
+ XCOFF file format. The option is enabled by default.
----------------
jh7370 wrote:

```suggestion
 Do not demangle symbol names in the output. This option is only for ELF and
 XCOFF file formats. The option is enabled by default.
```
Sorry missed these points too. Not sure how.

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