[Macros] Fix duplicate diagnostics for macro attributes.

Type wrappers were invoking CustomAttrDeclRequest with a decl context
of the attached nominal type rather than its decl context, so the request
was invoked twice for the same custom attributes with different decl
contexts.

Author: hborla

lib/Sema/TypeCheckTypeWrapper.cpp

@@ -124,7 +124,9 @@ static void getTypeWrappers(NominalTypeDecl *decl,
   for (auto *attr : decl->getAttrs().getAttributes<CustomAttr>()) {
     auto *mutableAttr = const_cast<CustomAttr *>(attr);
     auto found = evaluateOrDefault(
-        ctx.evaluator, CustomAttrDeclRequest{mutableAttr, decl}, nullptr);
+        ctx.evaluator,
+        CustomAttrDeclRequest{mutableAttr, decl->getDeclContext()},
+        nullptr);
 
     if (!found)
       continue;

test/Macros/attached_macros_diags.swift

@@ -6,16 +6,15 @@
 
 @attached(accessor) macro m2(_: Int) -> Void = #externalMacro(module: "MyMacros", type: "Macro2")
 // expected-warning@-1{{external macro implementation type 'MyMacros.Macro2' could not be found for macro 'm2'}}
-// expected-note@-2 2{{candidate has partially matching parameter list (Int)}}
+// expected-note@-2{{candidate has partially matching parameter list (Int)}}
 
 @attached(accessor) macro m2(_: Double) -> Void = #externalMacro(module: "MyMacros", type: "Macro2")
 // expected-warning@-1{{external macro implementation type 'MyMacros.Macro2' could not be found for macro 'm2'}}
-// expected-note@-2 2{{candidate has partially matching parameter list (Double)}}
+// expected-note@-2{{candidate has partially matching parameter list (Double)}}
 
 @m1 struct X1 { }
 
-// FIXME: Redundant diagnostic
-@m2 struct X2 { } // expected-error 2{{no exact matches in call to macro 'm2'}}
+@m2 struct X2 { } // expected-error{{no exact matches in call to macro 'm2'}}
 
 // Check for nesting rules.
 struct SkipNestedType {