ModuleInterface: Don't alias Foundation module in swiftinterfaces.

Skip aliasing Foundation when `-alias-module-names-in-module-interface` is
specified since it appears to confuse the typechecker. The module name
"Foundation" is hardcoded and checked in several places, so aliasing Foundation
may be changing some subtle behaviors.

Resolves rdar://128897610.

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -97,6 +97,10 @@ static void printToolVersionAndFlagsComment(raw_ostream &out,
           importedName == BUILTIN_NAME)
         continue;
 
+      // Aliasing Foundation confuses the typechecker (rdar://128897610).
+      if (importedName == "Foundation")
+        continue;
+
       if (AliasModuleNamesTargets.insert(importedName).second) {
         out << " -module-alias " << MODULE_DISAMBIGUATING_PREFIX <<
                importedName << "=" << importedName;