Files test.cmx and …/opam/mtime_clock.cmxa make inconsistent assumptions over interface Mtime_clock

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The following fails in a 4.14 switch with flambda:

% cat test.ml
let _ = Mtime_clock.now_ns ()
% ocamlbuild -pkg mtime.clock -pkg mtime.clock.os test.native --
+ /home/fabian/.opam/4.14.0/bin/ocamlopt.opt -I /home/fabian/.opam/4.14.0/lib/mtime -I /home/fabian/.opam/4.14.0/lib/mtime/clock -I /home/fabian/.opam/4.14.0/lib/mtime/clock/os /home/fabian/.opam/4.14.0/lib/mtime/mtime.cmxa /home/fabian/.opam/4.14.0/lib/mtime/clock/os/mtime_clock.cmxa test.cmx -o test.native
File "_none_", line 1:
Error: Files test.cmx
       and /home/fabian/.opam/4.14.0/lib/mtime/clock/os/mtime_clock.cmxa
       make inconsistent assumptions over interface Mtime_clock
Command exited with code 2.

(removing -pkg mtime.clock fixes the issue, but it looks like there are some conflicting files in the installation, so I figured I'd raise it just in case)