demangler: Templated lambda demangling

demangler: Templated lambda demangling

Templated lambdas have a template-head, which is part of their
signature.  GCC ABI 18 mangles that into the lambda name.  This adds
support to the demangler.  We have to introduce artificial template
parameter names, as we need to refer to them from later components of
the lambda signature. We use $T:n, $N:n and $TT:n for type, non-type
and template parameters.  Non-type parameter names are not shown in
the strictly correct location -- for instance 'int (&NT) ()' would be
shown as 'int (&) $N:n'.  That's unfortunate, but an orthogonal issue.
The 'is_lambda_arg' field is now repurposed as indicating the number
of explicit template parameters (1-based).

	include/
	* demangle.h (enum demangle_component_type): Add
	DEMANGLE_COMPONENT_TEMPLATE_HEAD,
	DEMANGLE_COMPONENT_TEMPLATE_TYPE_PARM,
	DEMANGLE_COMPONENT_TEMPLATE_NON_TYPE_PARM,
	DEMANGLE_COMPONENT_TEMPLATE_TEMPLATE_PARM,
	DEMANGLE_COMPONENT_TEMPLATE_PACK_PARM.
	libiberty/
	* cp-demangle.c (struct d_print_info): Rename is_lambda_arg to
	lambda_tpl_parms.  Augment semantics.
	(d_make_comp): Add checks for new components.
	(d_template_parm, d_template_head): New.
	(d_lambda): Add templated lambda support.
	(d_print_init): Adjust.
	(d_print_lambda_parm_name): New.
	(d_print_comp_inner): Support templated lambdas,
	* testsuite/demangle-expected: Add testcases.