library: ensure any 'flags' is consistently 'unsigned'

library: ensure any 'flags' is consistently 'unsigned'

This commit is an outgrowth of the research into a bug
that recently surfaced with the 'w' program. And while
that program was just a victim several inconsistencies
were found in the handling of library flags during the
research. This patch just address such irregularities.

Reference(s):
http://www.freelists.org/post/procps/newlib-at-the-precipice,4

Signed-off-by: Jim Warner <james.warner@comcast.net>