[CS] Correctly set compound bit for UnresolvedMemberExprs

Now that IUOs are supported for compound function
references, we can properly set the compound bit
here.

This is a source breaking change since this used
to be legal:

```swift
struct S {
  static func foo(x: Int) -> Self { .init() }
}
let _: S = .foo(x:)(x: 0)
```

However I somewhat doubt anyone is intentionally
writing code like that.

Author: hamishknight

include/swift/AST/Expr.h

@@ -1898,18 +1898,7 @@ class UnresolvedMemberExpr final
                        bool implicit)
     : Expr(ExprKind::UnresolvedMember, implicit), DotLoc(dotLoc),
       NameLoc(nameLoc), Name(name) {
-    // FIXME(FunctionRefInfo): Really, we should be passing `nameLoc` directly,
-    // allowing the FunctionRefInfo to be treated as compound. This would
-    // require us to enable IUOs for compound names, e.g:
-    // ```
-    // struct S {
-    //   static func makeS(_: Int) -> S! { S() }
-    // }
-    //
-    // let s: S = .makeS(_:)(0)
-    // ```
-    setFunctionRefInfo(
-        FunctionRefInfo::unapplied(DeclNameLoc(nameLoc.getBaseNameLoc())));
+    setFunctionRefInfo(FunctionRefInfo::unapplied(nameLoc));
   }
 
   DeclNameRef getName() const { return Name; }

test/Constraints/members.swift

@@ -837,3 +837,13 @@ do {
     // expected-note@-2 {{cast 'Any' to 'AnyObject' or use 'as!' to force downcast to a more specific type to access members}}
   }
 }
+
+func testCompoundLeadingDot() {
+  struct S {
+    static func foo(x: Int) -> Self { .init() }
+  }
+
+  // Make sure we correctly strip the argument label.
+  let _: S = .foo(x:)(0)
+  let _: S = .foo(x:)(x: 0) // expected-error {{extraneous argument label 'x:' in call}}
+}

test/expr/primary/unqualified_name.swift

@@ -46,7 +46,7 @@ struct S0 {
 }
 
 // Determine context from type.
-let s0_static: S0 = .f3(_:y:z:)(0, y: 0, z: 0)
+let s0_static: S0 = .f3(_:y:z:)(0, 0, 0)
 
 class C0 {
   init(x: Int, y: Int, z: Int) { }