Expose POSIX functions incorporated into C23

C23 has incoporated a small number of POSIX functions, so these
should be exposed for C23, regardless of POSIX.

Reviewed by:	imp, emaste
Differential Revision:	https://reviews.freebsd.org/D47856

(cherry picked from commit 59677ae)

include/string.h

@@ -52,7 +52,7 @@ typedef	__size_t	size_t;
 #endif
 
 __BEGIN_DECLS
-#if __XSI_VISIBLE >= 600
+#if __XSI_VISIBLE >= 600 || __ISO_C_VISIBLE >= 2023
 void	*memccpy(void * __restrict, const void * __restrict, int, size_t);
 #endif
 void	*memchr(const void *, int, size_t) __pure;
@@ -86,7 +86,7 @@ int	 strcmp(const char *, const char *) __pure;
 int	 strcoll(const char *, const char *);
 char	*strcpy(char * __restrict, const char * __restrict);
 size_t	 strcspn(const char *, const char *) __pure;
-#if __POSIX_VISIBLE >= 200112 || __XSI_VISIBLE
+#if __POSIX_VISIBLE >= 200112 || __XSI_VISIBLE || __ISO_C_VISIBLE >= 2023
 char	*strdup(const char *) __malloc_like;
 #endif
 char	*strerror(int);
@@ -104,8 +104,10 @@ void	 strmode(int, char *);
 char	*strncat(char * __restrict, const char * __restrict, size_t);
 int	 strncmp(const char *, const char *, size_t) __pure;
 char	*strncpy(char * __restrict, const char * __restrict, size_t);
-#if __POSIX_VISIBLE >= 200809
+#if __POSIX_VISIBLE >= 200809 || __ISO_C_VISIBLE >= 2023
 char	*strndup(const char *, size_t) __malloc_like;
+#endif
+#if __POSIX_VISIBLE >= 200809
 size_t	 strnlen(const char *, size_t) __pure;
 #endif
 #if __BSD_VISIBLE

include/time.h

@@ -157,6 +157,8 @@ int clock_nanosleep(clockid_t, int, const struct timespec *, struct timespec *);
 #if __POSIX_VISIBLE >= 199506
 char *asctime_r(const struct tm *, char *);
 char *ctime_r(const time_t *, char *);
+#endif
+#if __POSIX_VISIBLE >= 199506 || __ISO_C_VISIBLE >= 2023
 struct tm *gmtime_r(const time_t *, struct tm *);
 struct tm *localtime_r(const time_t *, struct tm *);
 #endif