Unfortunately, "native" GHC advertises support for `JavaScriptFFI` even though
it doesn't support it. See also https://ghc.haskell.org/ticket/11214 for respective
bug.

However, in order to properly declare that packages require `JavaScriptFFI` support
via `other-extensions` we need to fixup the list of extensions fed to the cabal solver.

This patch does something similiar to the workaround we added some time ago to
filter out TemplateHaskell for older GHCs which didn't properly advertise
`TemplateHaskell` availability (c.f. 9f68eb44)