C++ Structured bindings have a mangling that has yet to be formally
documented. However, it's been around for a while and shows up for
module support.
include/
* demangle.h (enum demangle_component_type): Add
DEMANGLE_COMPONENT_STRUCTURED_BINDING.
libiberty/
* cp-demangle.c (d_make_comp): Adjust.
(d_unqualified_name): Add 'DC' support.
(d_count_template_scopes): Adjust.
(d_print_comp_inner): Add structured binding.
* testsuite/demangle-expected: Add testcases.