Providing --with-ocaml-libdir for ./configure. The default is the

stdlib if it's beneath --prefix, and is libdir/ocaml otherwise.

If someone has a better way than this to test whether $B is a path
within $A, I'd love to hear it:

  if test "$A" \< "$B" -a "$B" \< "${A}~"

llvm-svn: 42532