libc: bsort_s() requires both BSD_VISIBLE and EXT1_VISIBLE

Fixes build of Python:
/usr/include/stdlib.h:409:1: error: unknown type name 'errno_t'
errno_t bsort_s(void *, rsize_t, rsize_t,

Reported by: vishwin@
MFC after: 1 week
Sponsored by: NVIDIA Networking
Differential Revision: https://reviews.freebsd.org/D36493