libmagic: Unbreak for older FreeBSD releases.

byteswap.h is introduced in FreeBSD 13.2 but was not available in
earlier versions.  In order to support upgrading from an earlier
FreeBSD release we would need to tell the build system that fact.

PR:		bin/273736
Reported by:	philip
MFC after:	3 days

lib/libmagic/config.h

@@ -1,6 +1,9 @@
 /* config.h.  Generated from config.h.in by configure.  */
 /* config.h.in.  Generated from configure.ac by autoheader.  */
 
+/* FreeBSD */
+#include <osreldate.h>
+
 /* Define if building universal (internal helper macro) */
 /* #undef AC_APPLE_UNIVERSAL_BUILD */
 
@@ -21,8 +24,10 @@
 
 /* Define to 1 if you have the <byteswap.h> header file. */
 #ifndef __APPLE__ /* Cross building tools on macOS */
+#if __FreeBSD_version >= 1400079 || (__FreeBSD_version < 1400000 && __FreeBSD_version >= 1302500)
 #define HAVE_BYTESWAP_H 1
 #endif
+#endif
 
 /* Define to 1 if you have the <bzlib.h> header file. */
 /* #undef HAVE_BZLIB_H */