libcamlstr

- Deal with the libstr/libcamlstr issue by passing str.cmxa to the OCaml
  linker and -lcamlstr to the C linker. I suspect it is not very idiomatic.
I blame someone else
Merge branch 'libcamlstr'

This fixes the stupid problem with libstr/libcamlstr (won't build on
OCaml >=3.12 without this).