[lldb] Avoid unhandled Error in TypeSystemMap::GetTypeSystemForLanguage

When assertions are turned off, the `llvm::Error` value created at the
start of this function is overwritten using the move-assignment
operator, but the success value is never checked. Whenever a TypeSystem
cannot be found or created, this can lead to lldb core dumping with:

    Program aborted due to an unhandled Error:
    Error value was Success. (Note: Success values must still be checked prior to being destroyed).

Fix this by not creating a `llvm::Error` value in advance, and directly
returning the result of `llvm::make_error` instead, whenever an error is
encountered.

See also: <https://bugs.freebsd.org/253881> and
<https://bugs.freebsd.org/257829>.

Reviewed By: teemperor

Differential Revision: https://reviews.llvm.org/D108088

Author: DimitryAndric

lldb/source/Symbol/TypeSystem.cpp

@@ -223,70 +223,56 @@ void TypeSystemMap::ForEach(std::function<bool(TypeSystem *)> const &callback) {
 llvm::Expected<TypeSystem &> TypeSystemMap::GetTypeSystemForLanguage(
     lldb::LanguageType language,
     llvm::Optional<CreateCallback> create_callback) {
-  llvm::Error error = llvm::Error::success();
-  assert(!error); // Check the success value when assertions are enabled
   std::lock_guard<std::mutex> guard(m_mutex);
-  if (m_clear_in_progress) {
-    error = llvm::make_error<llvm::StringError>(
+  if (m_clear_in_progress)
+    return llvm::make_error<llvm::StringError>(
         "Unable to get TypeSystem because TypeSystemMap is being cleared",
         llvm::inconvertibleErrorCode());
-  } else {
-    collection::iterator pos = m_map.find(language);
-    if (pos != m_map.end()) {
-      auto *type_system = pos->second.get();
-      if (type_system) {
-        llvm::consumeError(std::move(error));
-        return *type_system;
-      }
-      error = llvm::make_error<llvm::StringError>(
-          "TypeSystem for language " +
-              llvm::StringRef(Language::GetNameForLanguageType(language)) +
-              " doesn't exist",
-          llvm::inconvertibleErrorCode());
-      return std::move(error);
-    }
 
-    for (const auto &pair : m_map) {
-      if (pair.second && pair.second->SupportsLanguage(language)) {
-        // Add a new mapping for "language" to point to an already existing
-        // TypeSystem that supports this language
-        m_map[language] = pair.second;
-        if (pair.second.get()) {
-          llvm::consumeError(std::move(error));
-          return *pair.second.get();
-        }
-        error = llvm::make_error<llvm::StringError>(
-            "TypeSystem for language " +
-                llvm::StringRef(Language::GetNameForLanguageType(language)) +
-                " doesn't exist",
-            llvm::inconvertibleErrorCode());
-        return std::move(error);
-      }
-    }
+  collection::iterator pos = m_map.find(language);
+  if (pos != m_map.end()) {
+    auto *type_system = pos->second.get();
+    if (type_system)
+      return *type_system;
+    return llvm::make_error<llvm::StringError>(
+        "TypeSystem for language " +
+            llvm::StringRef(Language::GetNameForLanguageType(language)) +
+            " doesn't exist",
+        llvm::inconvertibleErrorCode());
+  }
 
-    if (!create_callback) {
-      error = llvm::make_error<llvm::StringError>(
-          "Unable to find type system for language " +
-              llvm::StringRef(Language::GetNameForLanguageType(language)),
-          llvm::inconvertibleErrorCode());
-    } else {
-      // Cache even if we get a shared pointer that contains a null type system
-      // back
-      TypeSystemSP type_system_sp = (*create_callback)();
-      m_map[language] = type_system_sp;
-      if (type_system_sp.get()) {
-        llvm::consumeError(std::move(error));
-        return *type_system_sp.get();
-      }
-      error = llvm::make_error<llvm::StringError>(
+  for (const auto &pair : m_map) {
+    if (pair.second && pair.second->SupportsLanguage(language)) {
+      // Add a new mapping for "language" to point to an already existing
+      // TypeSystem that supports this language
+      m_map[language] = pair.second;
+      if (pair.second.get())
+        return *pair.second.get();
+      return llvm::make_error<llvm::StringError>(
           "TypeSystem for language " +
               llvm::StringRef(Language::GetNameForLanguageType(language)) +
               " doesn't exist",
           llvm::inconvertibleErrorCode());
     }
   }
 
-  return std::move(error);
+  if (!create_callback)
+    return llvm::make_error<llvm::StringError>(
+        "Unable to find type system for language " +
+            llvm::StringRef(Language::GetNameForLanguageType(language)),
+        llvm::inconvertibleErrorCode());
+
+  // Cache even if we get a shared pointer that contains a null type system
+  // back
+  TypeSystemSP type_system_sp = (*create_callback)();
+  m_map[language] = type_system_sp;
+  if (type_system_sp.get())
+    return *type_system_sp.get();
+  return llvm::make_error<llvm::StringError>(
+      "TypeSystem for language " +
+          llvm::StringRef(Language::GetNameForLanguageType(language)) +
+          " doesn't exist",
+      llvm::inconvertibleErrorCode());
 }
 
 llvm::Expected<TypeSystem &>