Strip RTS flags, since we cant honor them

Issue that caused it:
#1725

the problem is that we cant honour the `+RTS` flags, since these need to
be known when GHC is started. However, HIE is the compiler and is
started before we load any component.
Therefore, these options for the different component are unusable and we
strip them here to avoid a bug.
This commit is inspired by
haskell/hie-bios#102

Author: fendor

hie-plugin-api/Haskell/Ide/Engine/Cradle.hs

@@ -543,7 +543,7 @@ cabalHelperAction proj env package root fp = do
         let fs' = getFlags comp
         let fs = map (fixImportDirs root) fs'
         let targets = getTargets comp relativeFp
-        let ghcOptions = fs ++ targets
+        let ghcOptions = removeRTS (fs ++ targets)
         debugm $ "Flags for \"" ++ fp ++ "\": " ++ show ghcOptions
         debugm $ "Component Infos: " ++ show comp
         return
@@ -556,6 +556,16 @@ cabalHelperAction proj env package root fp = do
         $ CradleError
           (ExitFailure 2)
           err
+  where
+  -- | Strip out any ["+RTS", ..., "-RTS"] sequences in the command string list.
+  removeRTS :: [String] -> [String]
+  removeRTS ("+RTS" : xs)  =
+    case dropWhile (/= "-RTS") xs of
+      [] -> []
+      (_ : ys) -> removeRTS ys
+  removeRTS (y:ys)         = y : removeRTS ys
+  removeRTS []             = []
+
 
 -- | Fix occurrences of "-i." to "-i<cradle-root-dir>"
 -- Flags obtained from cabal-helper are relative to the package