Workaround GHC #11214 by filtering JavaScriptFFI

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. 9f68eb4)

(cherry picked from commit 608517b)

Cabal/Distribution/Simple/GHC.hs

@@ -144,16 +144,21 @@ configure verbosity hcPath hcPkgPath conf0 = do
 
   ghcInfo <- Internal.getGhcInfo verbosity implInfo ghcProg
   let ghcInfoMap = M.fromList ghcInfo
+      extensions = -- workaround https://ghc.haskell.org/ticket/11214
+                   filterExt JavaScriptFFI $
+                   -- see 'filterExtTH' comment below
+                   filterExtTH $ extensions0
 
       -- starting with GHC 8.0, `TemplateHaskell` will be omitted from
       -- `--supported-extensions` when it's not available.
       -- for older GHCs we can use the "Have interpreter" property to
       -- filter out `TemplateHaskell`
-      extensions | ghcVersion < Version [8] []
-                 , Just "NO" <- M.lookup "Have interpreter" ghcInfoMap
-                   = filter ((/= EnableExtension TemplateHaskell) . fst)
-                     extensions0
-                 | otherwise = extensions0
+      filterExtTH | ghcVersion < Version [8] []
+                   , Just "NO" <- M.lookup "Have interpreter" ghcInfoMap
+                   = filterExt TemplateHaskell
+                  | otherwise = id
+
+      filterExt ext = filter ((/= EnableExtension ext) . fst)
 
   let comp = Compiler {
         compilerId         = CompilerId GHC ghcVersion,