Sync libiberty with upstream GCC.

Sync libiberty with upstream GCC.

libiberty/ChangeLog:

	PR demangler/80513
	* cp-demangle.c (d_number): Check for overflow.
	* cplus-dem.c (consume_count): Fix overflow check.
	(gnu_special): Check for underscore after thunk delta.
	* testsuite/demangle-expected: Add tests for overflows and invalid
	characters in thunks.

	* cp-demangle.c (MAX_RECURSION_COUNT): New constant.
	(struct d_print_info): Add recursion field.
	(d_print_init): Initialize recursion.
	(d_print_comp): Check and update d_print_info recursion depth.

	* cp-demangle.c (d_substitution): Return NULL if d_add_substitution
	fails.

	* cp-demangle.h (struct d_info): Remove did_subs field.
	* cp-demangle.c (struct d_info_checkpoint): Likewise.
	(d_template_param): Don't update did_subs.
	(d_substitution): Likewise.
	(d_checkpoint): Don't assign did_subs.
	(d_backtrack): Likewise.
	(cplus_demangle_init_info): Don't initialize did_subs.