Suppress warnings about @_unsafeInheritExecutor on _unsafeInheritExecutor_ functions

When inside the concurrency library, suppress the diagnostics about use
of the (deprecated) `@_unsafeInheritExecutor` for functions whose names
start with the "_unsafeInheritExecutor_" prefix that's used for
compatibility. This focuses the diagnostic on those places in the
concurrency library that might still need to introduce this hack.

Author: DougGregor

lib/Sema/TypeCheckAttr.cpp

@@ -7279,7 +7279,10 @@ void AttributeChecker::visitUnsafeInheritExecutorAttr(
   auto fn = cast<FuncDecl>(D);
   if (!fn->isAsyncContext()) {
     diagnose(attr->getLocation(), diag::inherits_executor_without_async);
-  } else {
+  } else if (fn->getBaseName().isSpecial() ||
+             !fn->getParentModule()->getName().str().equals("_Concurrency") ||
+             !fn->getBaseIdentifier().str()
+                .startswith("_unsafeInheritExecutor_")) {
     bool inConcurrencyModule = D->getDeclContext()->getParentModule()->getName()
         .str().equals("_Concurrency");
     auto diag = fn->diagnose(diag::unsafe_inherits_executor_deprecated);

test/Concurrency/unsafe_inherit_executor.swift

@@ -172,3 +172,7 @@ func unsafeCallerAvoidsNewLoop(clock: some Clock) async throws {
     throw MyError.fail
   }
 }
+
+@_unsafeInheritExecutor
+func _unsafeInheritExecutor_hacky() async { }
+// expected-warning@-1{{@_unsafeInheritExecutor attribute is deprecated; consider an 'isolated' parameter defaulted to '#isolation' instead}}