Implement P0012R1, Make exception specifications part of the type system.

Implement P0012R1, Make exception specifications part of the type system.

libiberty/
	* cp-demangle.c (is_fnqual_component_type): New.
	(d_encoding, d_print_comp_inner, d_print_mod_list): Use it.
	(FNQUAL_COMPONENT_CASE): New.
	(d_make_comp, has_return_type, d_print_comp_inner)
	(d_print_function_type): Use it.
	(next_is_type_qual): New.
	(d_cv_qualifiers, d_print_mod): Handle noexcept and throw-spec.
include/
	* demangle.h (enum demangle_component_type): Add
	DEMANGLE_COMPONENT_NOEXCEPT, DEMANGLE_COMPONENT_THROW_SPEC.