NFC: check ModuleDecl file invariant always

Author: kavon

include/swift/AST/Module.h

@@ -25,6 +25,7 @@
 #include "swift/AST/Import.h"
 #include "swift/AST/LookupKinds.h"
 #include "swift/AST/Type.h"
+#include "swift/Basic/Assertions.h"
 #include "swift/Basic/BasicSourceInfo.h"
 #include "swift/Basic/Compiler.h"
 #include "swift/Basic/Debug.h"
@@ -388,7 +389,7 @@ class ModuleDecl
   void setBypassResilience() { BypassResilience = true; }
 
   ArrayRef<FileUnit *> getFiles() {
-    assert(!Files.empty() || failedToLoad());
+    ASSERT(!Files.empty() || failedToLoad());
     return Files;
   }
   ArrayRef<const FileUnit *> getFiles() const {