Signed-off-by: Nmaweiye <maweiye@huawei.com>

at least a couple of these are used on BSD too, and the FNM_*
namespace is reserved in fnmatch.h anyway.

the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.

installation docs have also been updated to reflect this change.

note that none of these are implemented, and programs depending on
them may break... patch by sh4rm4