Assertion failure in the tests after merging in JSOO master

[OlivierNicole]

After merging the current jsoo-tip and jsoo-merge (following the instructions in #47) and running dune runtest --profile wasm, I get this error:

ile ".js/default/dynlink/_unknown_", line 1, characters 0-0:
Command [3] exited with code 125:
$ (cd _build/default/.js/default/dynlink && ../../../../install/default/bin/wasm_of_ocaml --source-map-inline -o dynlink.wasma /home/olivier/woo/_opam/lib/ocaml/dynlink/dynlink.cma)
../../../../install/default/bin/wasm_of_ocaml: You found a bug. Please report it at https://github.com/ocsigen/js_of_ocaml/issues :
Error: File "compiler/lib/wasm/wa_link.ml", line 617, characters 8-14: Assertion failed

The revision resulting from the merge can be found at https://github.com/ocaml-wasm/wasm_of_ocaml/tree/tmp-test-merge.

cc @vouillon

[OlivierNicole]

Very swift fix, thanks!