Passing host args to SpiderMonkey causes module tests to fail

[Ms2ger]

We end up running the shell with

    --module
    [hostarg]
    /tmp/HqmLu073pu5L64GWXI66/await-identifier-module-1.js

instead of

    [hostarg]
    --module
    /tmp/HqmLu073pu5L64GWXI66/await-identifier-module-1.js

causing

Error: can't open [hostarg]: No such file or directory

Fix to eshost incoming.