Test out perf impact of making Hasher resilient

Author: airspeedswift

stdlib/public/core/Hasher.swift

@@ -276,7 +276,6 @@ internal struct _BufferingHasher<Core: _HasherCore> {
 ///   different values on every new execution of your program. The hash
 ///   algorithm implemented by `Hasher` may itself change between any two
 ///   versions of the standard library.
-@_fixed_layout // FIXME: Should be resilient (rdar://problem/38549901)
 public struct Hasher {
   internal typealias RawCore = _SipHash13Core
   internal typealias Core = _BufferingHasher<RawCore>