demangler: C++ modules support
This adds demangling support for C++ modules. A new 'W' component
along with augmented behaviour of 'S' components.
include/
* demangle.h (enum demangle_component_type): Add module components.
libiberty/
* cp-demangle.c (d_make_comp): Adjust.
(d_name, d_prefix): Adjust subst handling. Add module handling.
(d_maybe_module_name): New.
(d_unqualified_name): Add incoming module parm. Handle it. Adjust all callers.
(d_special_name): Add 'GI' support.
(d_count_template_scopes): Adjust.
(d_print_comp_inner): Print module.
* testsuite/demangle-expected: New test cases