testsL fix py<libname> check

Reported-by: Bruce Dubbs <bruce.dubbs@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
build-sys: Use _POSIX_VERSION to determine support for %m

%m is included in POSIX 2008, so we can check if the libc implements
that before failing.

Signed-off-by: Karel Zak <kzak@redhat.com>
include: Add missing includes

sys/types.h: For u_char typedef
sys/params.h: For MAXNAMLEN
sys/ttydefaults.h: For various tty definitions (also add configure check)

Signed-off-by: Karel Zak <kzak@redhat.com>
build-sys: Check for type sighandler_t and use if present

__sighandler_t is libc implementation specific and should not be relied
upon. Instead, we fall back upon void (*)(int), as specified by POSIX.

Signed-off-by: Karel Zak <kzak@redhat.com>
build-sys: Fix check for __GNU_LIBRARY__

If we are not on glibc, __GNU_LIBRARY__ will not exist causing the check
to always fail and try to use syscalls directly.

Signed-off-by: Karel Zak <kzak@redhat.com>
agetty: use standard angular brackets in usage message

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
libfdisk: improve spelling of two comments

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
docs: tweak the grammar of an agetty man-page fragment

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
libfdisk: cleanup warning messages

Signed-off-by: Karel Zak <kzak@redhat.com>