Continuing the move to refer to C23 in place of C2X throughout the
source tree, update documentation, diagnostics, comments, variable and
function names, etc., to use the C23 name.

Testsuite updates are left for a future patch, except for testcases
that test diagnostics that previously mentioned C2X (but in those
testcases, sometimes other comments are updated, not just the
diagnostic expectations).

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

gcc/
	* builtins.def (DEF_C2X_BUILTIN): Rename to DEF_C23_BUILTIN and
	use flag_isoc23 and function_c23_misc.
	* config/rl78/rl78.cc (rl78_option_override): Compare
	lang_hooks.name with "GNU C23" not "GNU C2X".
	* coretypes.h (function_c2x_misc): Rename to function_c23_misc.
	* doc/cpp.texi (@code{__has_attribute}): Refer to C23 instead of
	C2x.
	* doc/extend.texi: Likewise.
	* doc/invoke.texi: Likewise.
	* dwarf2out.cc (highest_c_language, gen_compile_unit_die): Compare
	against and return "GNU C23" language string instead of "GNU C2X".
	* ginclude/float.h: Refer to C23 instead of C2X in comments.
	* ginclude/stdint-gcc.h: Likewise.
	* glimits.h: Likewise.
	* tree.h: Likewise.

gcc/ada/
	* gcc-interface/utils.cc (flag_isoc2x): Rename to flag_isoc23.

gcc/c-family/
	* c-common.cc (flag_isoc2x): Rename to flag_isoc23.
	(c_common_reswords): Use D_C23 instead of D_C2X.
	* c-common.h: Refer throughout to C23 instead of C2X in comments.
	(D_C2X): Rename to D_C23.
	(flag_isoc2x): Rename to flag_isoc23.
	* c-cppbuiltin.cc (builtin_define_float_constants): Use
	flag_isoc23 instead of flag_isoc2x.  Refer to C23 instead of C2x
	in comments.
	* c-format.cc: Use STD_C23 instead of STD_C2X and flag_isoc23
	instead of flag_isoc2x.  Refer to C23 instead of C2X in comments.
	* c-format.h: Use STD_C23 instead of STD_C2X.
	* c-lex.cc: Use warn_c11_c23_compat instead of warn_c11_c2x_compat
	and flag_isoc23 instead of flag_isoc2x.  Refer to C23 instead of
	C2X in diagnostics.
	* c-opts.cc: Use flag_isoc23 instead of flag_isoc2x.  Refer to C23
	instead of C2X in comments.
	(set_std_c2x): Rename to set_std_c23.
	* c.opt (Wc11-c23-compat): Use CPP(cpp_warn_c11_c23_compat)
	CppReason(CPP_W_C11_C23_COMPAT) Var(warn_c11_c23_compat) instead
	of CPP(cpp_warn_c11_c2x_compat) CppReason(CPP_W_C11_C2X_COMPAT)
	Var(warn_c11_c2x_compat).

gcc/c/
	* c-decl.cc: Use flag_isoc23 instead of flag_isoc2x and c23_auto_p
	instead of c2x_auto_p.  Refer to C23 instead of C2X in diagnostics
	and comments.
	* c-errors.cc: Use flag_isoc23 instead of flag_isoc2x and
	warn_c11_c23_compat instead of warn_c11_c2x_compat.  Refer to C23
	instead of C2X in comments.
	* c-parser.cc: Use flag_isoc23 instead of flag_isoc2x,
	warn_c11_c23_compat instead of warn_c11_c2x_compat, c23_auto_p
	instead of c2x_auto_p and D_C23 instead of D_C2X.  Refer to C23
	instead of C2X in diagnostics and comments.
	* c-tree.h: Refer to C23 instead of C2X in comments.
	(struct c_declspecs): Rename c2x_auto_p to c23_auto_p.
	* c-typeck.cc: Use flag_isoc23 instead of flag_isoc2x and
	warn_c11_c23_compat instead of warn_c11_c2x_compat.  Refer to C23
	instead of C2X in diagnostics and comments.

gcc/fortran/
	* gfortran.h (gfc_real_info): Refer to C23 instead of C2X in
	comment.

gcc/lto/
	* lto-lang.cc (flag_isoc2x): Rename to flag_isoc23.

gcc/testsuite/
	* gcc.dg/binary-constants-2.c: Refer to C23 instead of C2X.
	* gcc.dg/binary-constants-3.c: Likewise.
	* gcc.dg/bitint-23.c: Likewise.
	* gcc.dg/bitint-26.c: Likewise.
	* gcc.dg/bitint-27.c: Likewise.
	* gcc.dg/c11-attr-syntax-1.c: Likewise.
	* gcc.dg/c11-attr-syntax-2.c: Likewise.
	* gcc.dg/c11-floatn-1.c: Likewise.
	* gcc.dg/c11-floatn-2.c: Likewise.
	* gcc.dg/c11-floatn-3.c: Likewise.
	* gcc.dg/c11-floatn-4.c: Likewise.
	* gcc.dg/c11-floatn-5.c: Likewise.
	* gcc.dg/c11-floatn-6.c: Likewise.
	* gcc.dg/c11-floatn-7.c: Likewise.
	* gcc.dg/c11-floatn-8.c: Likewise.
	* gcc.dg/c2x-attr-syntax-4.c: Likewise.
	* gcc.dg/c2x-attr-syntax-6.c: Likewise.
	* gcc.dg/c2x-attr-syntax-7.c: Likewise.
	* gcc.dg/c2x-binary-constants-2.c: Likewise.
	* gcc.dg/c2x-floatn-5.c: Likewise.
	* gcc.dg/c2x-floatn-6.c: Likewise.
	* gcc.dg/c2x-floatn-7.c: Likewise.
	* gcc.dg/c2x-floatn-8.c: Likewise.
	* gcc.dg/c2x-nullptr-4.c: Likewise.
	* gcc.dg/c2x-qual-2.c: Likewise.
	* gcc.dg/c2x-qual-3.c: Likewise.
	* gcc.dg/c2x-qual-6.c: Likewise.
	* gcc.dg/cpp/c11-warning-1.c: Likewise.
	* gcc.dg/cpp/c11-warning-2.c: Likewise.
	* gcc.dg/cpp/c11-warning-3.c: Likewise.
	* gcc.dg/cpp/c2x-warning-2.c: Likewise.
	* gcc.dg/cpp/gnu11-elifdef-3.c: Likewise.
	* gcc.dg/cpp/gnu11-elifdef-4.c: Likewise.
	* gcc.dg/cpp/gnu11-warning-1.c: Likewise.
	* gcc.dg/cpp/gnu11-warning-2.c: Likewise.
	* gcc.dg/cpp/gnu11-warning-3.c: Likewise.
	* gcc.dg/cpp/gnu2x-warning-2.c: Likewise.
	* gcc.dg/dfp/c11-constants-1.c: Likewise.
	* gcc.dg/dfp/c11-constants-2.c: Likewise.
	* gcc.dg/dfp/c2x-constants-2.c: Likewise.
	* gcc.dg/dfp/constants-pedantic.c: Likewise.
	* gcc.dg/pr30260.c: Likewise.
	* gcc.dg/system-binary-constants-1.c: Likewise.

libcpp/
	* directives.cc: Refer to C23 instead of C2X in diagnostics and
	comments.
	(STDC2X): Rename to STDC23.
	* expr.cc: Use cpp_warn_c11_c23_compat instead of
	cpp_warn_c11_c2x_compat and CPP_W_C11_C23_COMPAT instead of
	CPP_W_C11_C2X_COMPAT.  Refer to C23 instead of C2X in diagnostics
	and comments.
	* include/cpplib.h: Refer to C23 instead of C2X in diagnostics and
	comments.
	(CLK_GNUC2X): Rename to CLK_GNUC23.
	(CLK_STDC2X): Rename to CLK_STDC23.
	(CPP_W_C11_C2X_COMPAT): Rename to CPP_W_C11_C23_COMPAT.
	* init.cc: Use GNUC23 instead of GNUC2X, STDC23 instead of STDC2X
	and cpp_warn_c11_c23_compat instead of cpp_warn_c11_c2x_compat.
	* lex.cc (maybe_va_opt_error): Refer to C23 instead of C2X in
	diagnostic.
	* macro.cc (_cpp_arguments_ok): Refer to C23 instead of C2X in
	comment.