[Serialization] Stop storing the load Status in ModuleFile itself

The code tried extra hard to make sure this stayed in sync with the
returned ValidationInfo, but there's no real reason for that. Just
keep a single "HasError" bit for checking that the module's not being
obviously misused. (I snuck some groundwork for this into the previous
commit.)

lib/Serialization/ModuleFile.cpp

@@ -1242,7 +1242,7 @@ ModuleFile::ModuleFile(
     : ModuleInputBuffer(std::move(moduleInputBuffer)),
       ModuleDocInputBuffer(std::move(moduleDocInputBuffer)),
       DeserializedTypeCallback([](Type ty) {}) {
-  assert(getStatus() == Status::Valid);
+  assert(!hasError());
   Bits.IsFramework = isFramework;
 
   PrettyStackTraceModuleFile stackEntry(*this);
@@ -1490,7 +1490,7 @@ Status ModuleFile::associateWithFileContext(FileUnit *file,
                                             bool treatAsPartialModule) {
   PrettyStackTraceModuleFile stackEntry(*this);
 
-  assert(getStatus() == Status::Valid && "invalid module file");
+  assert(!hasError() && "error already detected; should not call this");
   assert(!FileContext && "already associated with an AST module");
   FileContext = file;
 
@@ -1612,11 +1612,11 @@ Status ModuleFile::associateWithFileContext(FileUnit *file,
                                                            None);
   }
 
-  return getStatus();
+  return Status::Valid;
 }
 
 std::unique_ptr<llvm::MemoryBuffer> ModuleFile::takeBufferForDiagnostics() {
-  assert(getStatus() != Status::Valid);
+  assert(hasError());
 
   // Today, the only buffer that might have diagnostics in them is the input
   // buffer, and even then only if it has imported module contents.