ModuleInterface: Print imports with @preconcurrency in swiftinterface files.

When a module has been imported `@preconcurrency` in source, when it is printed
in a `swiftinterface` file it should be printed along with the attribute to
ensure that type checking of the module's public declarations behaves
consistently.

This fix is a little unsatisfying because it adds another a linear scan over
all imports in the source for each printed import. This should be improved, but
it can be done later.

Resolves rdar://136857313.

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -271,6 +271,9 @@ static void printImports(raw_ostream &out,
       ModuleDecl::ImportFilterKind::Default,
       ModuleDecl::ImportFilterKind::ShadowedByCrossImportOverlay};
 
+  // FIXME: Scan over all imports in the module once to build up the attribute
+  // set for printed imports, instead of repeatedly doing linear scans for each
+  // kind of attribute.
   using ImportSet = llvm::SmallSet<ImportedModule, 8, ImportedModule::Order>;
   auto getImports = [M](ModuleDecl::ImportFilter filter) -> ImportSet {
     SmallVector<ImportedModule, 8> matchingImports;
@@ -355,6 +358,9 @@ static void printImports(raw_ostream &out,
         out << "@_spi(" << spiName << ") ";
     }
 
+    if (M->isModuleImportedPreconcurrency(importedModule))
+      out << "@preconcurrency ";
+
     if (Opts.printPackageInterface() &&
         !publicImportSet.count(import) &&
         packageOnlyImportSet.count(import))