MFC r269077 (sbruno): libstand qdivrem warning fixes

MFC r269077 (sbruno): libstand qdivrem warning fixes

  libstand's qdivrem.c assumes that sizeof(int) == sizeof(long), this is not
  true on amd64 I'm not quite positive this is the "correct" solution for
  this but it does seem to compile and shut up the spew of warnings when
  compiling libstand for userboot.

  Add two _Static_asserts() so that in the future somebody will get a compile
  failure if an architecture develops that violates the assumptions of this
  code. (strongly suggested by jmg)

  Change commetns to indicate int types instead of long.  (noted by ian in
  phabric review)

  Phabric:    https://phabric.freebsd.org/D443

git-svn-id: svn://svn.freebsd.org/base/stable/10@271134 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f