c-family, docs: Adjust descriptions/documentation for C23 publication

As C23 has been published already https://www.iso.org/standard/82075.html
we don't need to say that it is expected to be published etc.

Furthermore, standards.texi was still documenting that -std=gnu17
is the default.

2024-11-21  Jakub Jelinek  <jakub@redhat.com>

gcc/
	* doc/invoke.texi (-std=c23): Adjust documentation for
	publication of the ISO/IEC 9899:2024 standard.
	* doc/standards.texi: Likewise.  Document -std=gnu17 and
	-std=gnu23 options.  Mention that -std=gnu23 rather than
	-std=gnu17 is now the default for C.
gcc/c-family/
	* c.opt (std=c23, std=gnu23, std=iso9899:2024): Adjust description
	for publication of the ISO/IEC 9899:2024 standard.

gcc/c-family/c.opt

@@ -2605,7 +2605,7 @@ Conform to the ISO 2017 C standard (published in 2018).
 
 std=c23
 C ObjC
-Conform to the ISO 2023 C standard draft (expected to be published in 2024).
+Conform to the ISO 2023 C standard (published in 2024).
 
 std=c2x
 C ObjC Alias(std=c23)
@@ -2707,7 +2707,7 @@ Conform to the ISO 2017 C standard (published in 2018) with GNU extensions.
 
 std=gnu23
 C ObjC
-Conform to the ISO 2023 C standard draft (expected to be published in 2024) with GNU extensions.
+Conform to the ISO 2023 C standard (published in 2024) with GNU extensions.
 
 std=gnu2x
 C ObjC Alias(std=gnu23)
@@ -2763,7 +2763,7 @@ Conform to the ISO 2017 C standard (published in 2018).
 
 std=iso9899:2024
 C ObjC Alias(std=c23)
-Conform to the ISO 2023 C standard draft (expected to be published in 2024).
+Conform to the ISO 2023 C standard (published in 2024).
 
 stdlib=
 Driver C++ ObjC++ Common Condition(ENABLE_STDLIB_OPTION) Var(flag_stdlib_kind) Joined Enum(stdlib_kind) RejectNegative Init(1)

gcc/doc/invoke.texi

@@ -2479,8 +2479,8 @@ applied with @option{-std=c11}) and a new value of
 @item c23
 @itemx c2x
 @itemx iso9899:2024
-ISO C23, the 2023 revision of the ISO C standard (expected to be
-published in 2024).  The name @samp{c2x} is deprecated.
+ISO C23, the 2023 revision of the ISO C standard (published in 2024).  The
+name @samp{c2x} is deprecated.
 @item c2y
 The next version of the ISO C standard, still under development.  The

gcc/doc/standards.texi

@@ -115,8 +115,8 @@ known as @dfn{C17} and is supported with @option{-std=c17} or
 @option{-std=c11}, and the only difference between the options is the
 value of @code{__STDC_VERSION__}.
 
-A fifth version of the C standard, known as @dfn{C23}, is
-expected to be published in 2024 as ISO/IEC 9899:2024.
+A fifth version of the C standard, known as @dfn{C23}, was published
+in 2024 as ISO/IEC 9899:2024.
 (While in development, drafts of this standard version were referred
 to as @dfn{C2X}.)  Support for this is
 enabled with @option{-std=c23} or @option{-std=iso9899:2024}.
@@ -136,11 +136,12 @@ Use of the
 they conflict with the C standard version selected.  You may also
 select an extended version of the C language explicitly with
 @option{-std=gnu90} (for C90 with GNU extensions), @option{-std=gnu99}
-(for C99 with GNU extensions) or @option{-std=gnu11} (for C11 with GNU
-extensions).  
+(for C99 with GNU extensions), @option{-std=gnu11} (for C11 with GNU
+extensions), @option{-std=gnu17} (for C17 with GNU extensions) or
+@option{-std=gnu23} (for C23 with GNU extensions).
 
 The default, if no C language dialect options are given,
-is @option{-std=gnu17}.
+is @option{-std=gnu23}.
 
 The ISO C standard defines (in clause 4) two classes of conforming
 implementation.  A @dfn{conforming hosted implementation} supports the