[Sema] Don't set FunctionRefKind::Compound for an implicit ~=

It's not clear to me why it was ever set this way,
but it prevents IUOs from working with the match
operator. Unset it, and let pre-checking correctly
assign it a `FunctionRefKind::SingleApply`.

Author: hamishknight

lib/Sema/TypeCheckPattern.cpp

@@ -781,10 +781,6 @@ ExprPatternMatchRequest::evaluate(Evaluator &evaluator,
       DeclNameLoc(EP->getLoc()));
   matchOp->setImplicit();
 
-  // FIXME: This matches what the previous code had, but it doesn't seems like
-  // it should be set to this.
-  matchOp->setFunctionRefKind(FunctionRefKind::Compound);
-
   // Note we use getEndLoc here to have the BinaryExpr source range be the same
   // as the expr pattern source range.
   auto *matchVarRef =

test/Constraints/patterns.swift

@@ -557,3 +557,10 @@ extension [EWithIdent<Int>] {
     }
   }
 }
+
+struct TestIUOMatchOp {
+  static func ~= (lhs: TestIUOMatchOp, rhs: TestIUOMatchOp) -> Bool! { nil }
+  func foo() {
+    if case self = self {}
+  }
+}