Use List.exists for contains (#1518)

* Use List.exists for contains

* ListSet.contains is List.exists

* Revert "ListSet.contains is List.exists"

This reverts commit dc41206f8ffd4ef047ade0eaf1ae200900609b11.

Author: forki

src/fsharp/autobox.fs

@@ -17,7 +17,7 @@ open Microsoft.FSharp.Compiler.TypeRelations
 // Decide the set of mutable locals to promote to heap-allocated reference cells
 
 type cenv = 
-    { g: TcGlobals; 
+    { g: TcGlobals
       amap: Import.ImportMap }
 
 /// Find all the mutable locals that escape a method, function or lambda expression

src/fsharp/lib.fs

@@ -178,14 +178,11 @@ module ListAssoc =
 //------------------------------------------------------------------------
 
 module ListSet = 
-    (* NOTE: O(n)! *)
-    let rec contains f x l = 
-        match l with 
-        | [] -> false
-        | x'::t -> f x x' || contains f x t
+    let inline contains f x l = List.exists (f x) l
 
     (* NOTE: O(n)! *)
     let insert f x l = if contains f x l then l else x::l
+
     let unionFavourRight f l1 l2 = 
         match l1, l2 with 
         | _, [] -> l1