The following patch implements the C++23 P2290R3 paper.

2022-08-20  Jakub Jelinek  <jakub@redhat.com>

	PR c++/106645
libcpp/
	* include/cpplib.h (struct cpp_options): Implement
	P2290R3 - Delimited escape sequences.  Add delimite_escape_seqs
	member.
	* init.cc (struct lang_flags): Likewise.
	(lang_defaults): Add delim column.
	(cpp_set_lang): Copy over delimite_escape_seqs.
	* charset.cc (extend_char_range): New function.
	(_cpp_valid_ucn): Use it.  Handle delimited escape sequences.
	(convert_hex): Likewise.
	(convert_oct): Likewise.
	(convert_ucn): Use extend_char_range.
	(convert_escape): Call convert_oct even for \o.
	(_cpp_interpret_identifier): Handle delimited escape sequences.
	* lex.cc (get_bidi_ucn_1): Likewise.  Add end argument, fill it in.
	(get_bidi_ucn): Adjust get_bidi_ucn_1 caller.  Use end argument to
	compute num_bytes.
gcc/testsuite/
	* c-c++-common/cpp/delimited-escape-seq-1.c: New test.
	* c-c++-common/cpp/delimited-escape-seq-2.c: New test.
	* c-c++-common/cpp/delimited-escape-seq-3.c: New test.
	* c-c++-common/Wbidi-chars-24.c: New test.
	* gcc.dg/cpp/delimited-escape-seq-1.c: New test.
	* gcc.dg/cpp/delimited-escape-seq-2.c: New test.
	* g++.dg/cpp/delimited-escape-seq-1.C: New test.
	* g++.dg/cpp/delimited-escape-seq-2.C: New test.