Handle several functions now being provided by glibc

We mention that these are now superseded by the glibc implementations,
make the headers cope with already declared functions on glibc-based
systems, and document this in the man pages.

include/bsd/stdlib.h

@@ -67,7 +67,9 @@ int sradixsort(const unsigned char **base, int nmemb,
                const unsigned char *table, unsigned endbyte);
 
 void *reallocf(void *ptr, size_t size);
+#if defined(_GNU_SOURCE) && defined(__GLIBC__) && !__GLIBC_PREREQ(2, 26)
 void *reallocarray(void *ptr, size_t nmemb, size_t size);
+#endif
 
 long long strtonum(const char *nptr, long long minval, long long maxval,
                    const char **errstr);

include/bsd/string.h

@@ -42,7 +42,9 @@ size_t strlcat(char *dst, const char *src, size_t siz);
 char *strnstr(const char *str, const char *find, size_t str_len);
 void strmode(mode_t mode, char *str);
 
+#if defined(_GNU_SOURCE) && defined(__GLIBC__) && !__GLIBC_PREREQ(2, 25)
 void explicit_bzero(void *buf, size_t len);
+#endif
 __END_DECLS
 
 #endif

man/explicit_bzero.3bsd

@@ -72,4 +72,5 @@ pass, making it useful for clearing sensitive memory such as a password.
 The
 .Fn explicit_bzero
 function first appeared in
-.Ox 5.5 .
+.Ox 5.5 ,
+glibc 2.25.

man/libbsd.7

@@ -150,13 +150,36 @@ function can be used.
 Otherwise the code needs to be prepared for neither of these functions being
 available.
 .El
+.Sh SUPERSEDED
+Some functions have been superseded by implementations in other system
+libraries, and might disappear on the next SONAME bump, assuming those
+other implementation have widespread deployment, or the implementations
+are present in all major
+.Nm libc
+for example.
 .Pp
-In addition, the MD5 set of digest funtions are now provided by the
+.Bl -tag -width 4m -compact
+.It Fn MD5Init
+.It Fn MD5Update
+.It Fn MD5Pad
+.It Fn MD5Final
+.It Fn MD5Transform
+.It Fn MD5End
+.It Fn MD5File
+.It Fn MD5FileChunk
+.It Fn MD5Data
+The set of MD5 digest functions are now provided by the
 .Nm libmd
-companion library, so it is advised to use that instead, as the ones
-provided in
-.Nm libbsd
-might disappear on the next SONAME bump.
+companion library, so it is advised to use that instead.
+.It Fn explicit_bzero
+This function is provided by
+.Nm glibc
+2.25.
+.It Fn reallocarray
+This function is provided by
+.Nm glibc
+2.26.
+.El
 .Sh SEE ALSO
 .Xr arc4random 3bsd ,
 .Xr bitstring 3bsd ,

man/reallocarray.3bsd

@@ -102,4 +102,5 @@ is set to
 .Sh HISTORY
 .Fn reallocarray
 appeared in
-.Ox 5.6 .
+.Ox 5.6 ,
+glibc 2.26.