[Binutils support] Add demangling to libiberty

[Iain Buclaw]

One of the binutils devs suggested this, to move D demangling 
into libiberty, that way binutils programs (and any other program 
that uses libiberty in a similar manner) will gain D support.

For binutils, this would include D demangling support for (via 
the -C or --demangle= switch).

- nm
- addr2line
- objdump
- ld

https://github.com/ibuclaw/gdb/commit/0ba7ac2f91f45b24bcfba2d1ecedb10580fac152

I have named the specified demangle style as 'dlang', if no one 
has objects, I'll go ahead and write it up.

Regards
Iain.