Since the merge of file 5.21 in r276415 and r276416, stable/9 and
stable/10 cannot be built from FreeBSD 8.x. This is because the
build-tools stage requires libmagic, but lib/libmagic/config.h was
generated on head, and it now enables using the xlocale.h APIs, which
are not supported on 8.x (and on 9.x before __FreeBSD_version 900506).
See also the start of this thread on -stable:
https://lists.freebsd.org/pipermail/freebsd-stable/2015-January/081521.html
To fix this, conditionalize the use of xlocale.h APIs to make
bootstrapping from older FreeBSD versions work correctly.
Reviewed by: delphij
Differential Revision: https://reviews.freebsd.org/D1518
f4d39872ad