[stdlib] SignedNumber to refine Comparable in Swift 3 mode (#9668)

Fixes: https://bugs.swift.org/browse/SR-4899

Author: moiseev

stdlib/public/core/Integers.swift.gyb

@@ -3495,7 +3495,7 @@ public typealias Integer = BinaryInteger
 public typealias IntegerArithmetic = BinaryInteger
 
 @available(swift, obsoleted: 4)
-public typealias SignedNumber = SignedNumeric
+public typealias SignedNumber = SignedNumeric & Comparable
 
 @available(swift, obsoleted: 4)
 public typealias AbsoluteValuable = SignedNumeric & Comparable