Add ModuleFile::isSIB

We can't make the same assumptions about .sib files.

Ideally, we should serialize the module's stage and set WasDeserializedCanonical
based on that state. However, we probably still want the IsSIB flag for
assertions.

lib/Serialization/ModuleFile.cpp

@@ -1115,6 +1115,7 @@ ModuleFile::ModuleFile(
       Name = info.name;
       TargetTriple = info.targetTriple;
       CompatibilityVersion = info.compatibilityVersion;
+      IsSIB = extInfo->isSIB();
 
       hasValidControlBlock = true;
       break;