libc: Add <stdio.h> C23 feature test macro

Define the __STDC_VERSION_STDIO_H__ feature test macro now that
the header fully conforms to C23.

Reviewed by:	fuz
Approved by:	fuz (mentor)
MFC after:	1 month
Differential Revision: https://reviews.freebsd.org/D58842

include/rpc/xdr.h

@@ -332,7 +332,7 @@ __BEGIN_DECLS
 extern void   xdrmem_create(XDR *, char *, u_int, enum xdr_op);
 
 /* XDR using stdio library */
-#ifdef _STDIO_H_
+#ifdef __STDC_VERSION_STDIO_H__
 extern void   xdrstdio_create(XDR *, FILE *, enum xdr_op);
 #endif
 

include/stdio.h

@@ -32,8 +32,8 @@
  * SUCH DAMAGE.
  */
 
-#ifndef	_STDIO_H_
-#define	_STDIO_H_
+#ifndef __STDC_VERSION_STDIO_H__
+#define __STDC_VERSION_STDIO_H__	202311L
 
 #include <sys/cdefs.h>
 #include <sys/_null.h>
@@ -540,4 +540,4 @@ extern int __isthreaded;
 __END_DECLS
 __NULLABILITY_PRAGMA_POP
 
-#endif /* !_STDIO_H_ */
+#endif /* !__STDC_VERSION_STDIO_H__ */

include/xlocale.h

@@ -68,7 +68,7 @@ __BEGIN_DECLS
 #include <xlocale/_ctype.h>
 #endif
 
-#ifdef _STDIO_H_
+#ifdef __STDC_VERSION_STDIO_H__
 #include <xlocale/_stdio.h>
 #endif
 

lib/libc/xdr/xdr.3

@@ -572,7 +572,7 @@ This routine returns the amount of memory required to encode
 using filter
 .Fa func .
 .Pp
-.It Li "#ifdef _STDIO_H_"
+.It Li "#ifdef __STDC_VERSION_STDIO_H__"
 .It Li "/* XDR using stdio library */"
 .It Xo
 .Ft void

lib/libgeom/libgeom.h

@@ -143,7 +143,7 @@ void geom_deletetree(struct gmesh *);
 
 struct gctl_req;
 
-#ifdef _STDIO_H_			/* limit #include pollution */
+#ifdef __STDC_VERSION_STDIO_H__		/* limit #include pollution */
 void gctl_dump(struct gctl_req *, FILE *);
 #endif
 void gctl_free(struct gctl_req *);

lib/libutil/libutil.h

@@ -151,7 +151,7 @@ int	uu_lock_txfr(const char *_ttyname, pid_t _pid);
  * Conditionally prototype the following functions if the include
  * files upon which they depend have been included.
  */
-#ifdef _STDIO_H_
+#ifdef __STDC_VERSION_STDIO_H__
 char	*fparseln(FILE *_fp, size_t *_len, size_t *_lineno,
 	    const char _delim[3], int _flags);
 #endif

stand/libsa/geli/geliboot_internal.h

@@ -28,9 +28,15 @@
 #ifndef _GELIBOOT_INTERNAL_H_
 #define _GELIBOOT_INTERNAL_H_
 
+/*
+ * XXX:
+ * The following deliberate defines are to keep g_eli.h from including
+ * unnecessary headers.  It would be preferable to conditionally include
+ * them in a _STANDALONE branch there instead.
+ */
 #define _STRING_H_
 #define _STRINGS_H_
-#define _STDIO_H_
+#define __STDC_VERSION_STDIO_H__	202311L
 
 #include <sys/endian.h>
 #include <sys/queue.h>