[stdlib] Add @_inlineable attribute with FIXME to hashValue implementations

Author: xwu

stdlib/public/core/ClosedRange.swift

@@ -168,7 +168,8 @@ extension ClosedRange.Index : Comparable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension ClosedRange.Index: Hashable
-where Bound: Strideable, Bound.Stride: SignedInteger, Bound: Hashable {
+  where Bound: Strideable, Bound.Stride: SignedInteger, Bound: Hashable {
+  @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {
     switch self {

stdlib/public/core/DropWhile.swift

@@ -188,11 +188,13 @@ extension LazyDropWhileCollection.Index: Equatable, Comparable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension LazyDropWhileCollection.Index: Hashable where Base.Index: Hashable {
+  @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {
     return base.hashValue
   }
 
+  @_inlineable // FIXME(sil-serialize-all)
   public func _hash(into hasher: inout _Hasher) {
     hasher.append(base)
   }

stdlib/public/core/Flatten.swift

@@ -233,6 +233,7 @@ extension FlattenCollection.Index : Comparable {
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension FlattenCollection.Index : Hashable
   where Base.Index : Hashable, Base.Element.Index : Hashable {
+  @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {
     return _hashValue(for: self)

stdlib/public/core/PrefixWhile.swift

@@ -208,11 +208,13 @@ extension LazyPrefixWhileCollection.Index: Comparable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension LazyPrefixWhileCollection.Index: Hashable where Base.Index: Hashable {
+  @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {
     return _hashValue(for: self)
   }
 
+  @_inlineable // FIXME(sil-serialize-all)
   public func _hash(into hasher: inout _Hasher) {
     switch _value {
     case .index(let value):