Add option for enabling/disabling parallel load

Add a setting to gate the new parallel dynamic library loading feature in the next diff. I followed the example of `lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp` and `lldb/source/Plugins/StructuredData/DarwinLog/StructuredDataDarwinLog.cpp` to create a scoped setting for the new feature.

NOTE: this setting defaults to FALSE.

Users should be able to enable the new feature as easily as adding a line to their .lldbinit file, or manually setting it in their session.

```
(lldb) apropos "POSIX dynamic"
No commands found pertaining to 'POSIX dynamic'. Try 'help' to see a complete list of debugger commands.

The following settings variables may relate to 'POSIX dynamic':
  plugin.dynamic-loader.posix-dyld.parallel-module-load -- Enable experimental loading of modules in parallel for the POSIX dynamic loader.
(lldb) settings show plugin.dynamic-loader.posix-dyld.parallel-module-load
plugin.dynamic-loader.posix-dyld.parallel-module-load (boolean) = false
(lldb) settings set plugin.dynamic-loader.posix-dyld.parallel-module-load true
(lldb) settings show plugin.dynamic-loader.posix-dyld.parallel-module-load
plugin.dynamic-loader.posix-dyld.parallel-module-load (boolean) = true
```

Author: Tom Yang

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/CMakeLists.txt

@@ -1,3 +1,11 @@
+lldb_tablegen(DynamicLoaderPOSIXDYLDProperties.inc -gen-lldb-property-defs
+  SOURCE DynamicLoaderPOSIXDYLDProperties.td
+  TARGET LLDBPluginDynamicLoaderPOSIXDYLDPropertiesGen)
+
+lldb_tablegen(DynamicLoaderPOSIXDYLDPropertiesEnum.inc -gen-lldb-property-enum-defs
+  SOURCE DynamicLoaderPOSIXDYLDProperties.td
+  TARGET LLDBPluginDynamicLoaderPOSIXDYLDPropertiesEnumGen)
+
 add_lldb_library(lldbPluginDynamicLoaderPosixDYLD PLUGIN
   DYLDRendezvous.cpp
   DynamicLoaderPOSIXDYLD.cpp
@@ -13,3 +21,7 @@ add_lldb_library(lldbPluginDynamicLoaderPosixDYLD PLUGIN
   LINK_COMPONENTS
     Support
   )
+
+add_dependencies(lldbPluginDynamicLoaderPosixDYLD
+  LLDBPluginDynamicLoaderPOSIXDYLDPropertiesGen
+  LLDBPluginDynamicLoaderPOSIXDYLDPropertiesEnumGen)

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp

@@ -34,9 +34,56 @@ using namespace lldb_private;
 
 LLDB_PLUGIN_DEFINE_ADV(DynamicLoaderPOSIXDYLD, DynamicLoaderPosixDYLD)
 
+namespace {
+
+#define LLDB_PROPERTIES_dynamicloaderposixdyld
+#include "DynamicLoaderPOSIXDYLDProperties.inc"
+
+enum {
+#define LLDB_PROPERTIES_dynamicloaderposixdyld
+#include "DynamicLoaderPOSIXDYLDPropertiesEnum.inc"
+};
+
+class PluginProperties : public Properties {
+public:
+  static llvm::StringRef GetSettingName() {
+    return DynamicLoaderPOSIXDYLD::GetPluginNameStatic();
+  }
+
+  PluginProperties() : Properties() {
+    m_collection_sp = std::make_shared<OptionValueProperties>(GetSettingName());
+    m_collection_sp->Initialize(g_dynamicloaderposixdyld_properties);
+  }
+
+  ~PluginProperties() override = default;
+
+  bool GetParallelModuleLoad() const {
+    const uint32_t idx = ePropertyParallelModuleLoad;
+    return GetPropertyAtIndexAs<bool>(idx, true);
+  }
+};
+
+} // namespace
+
+static PluginProperties &GetGlobalPluginProperties() {
+  static PluginProperties g_settings;
+  return g_settings;
+}
+
 void DynamicLoaderPOSIXDYLD::Initialize() {
   PluginManager::RegisterPlugin(GetPluginNameStatic(),
-                                GetPluginDescriptionStatic(), CreateInstance);
+                                GetPluginDescriptionStatic(), CreateInstance,
+                                &DebuggerInitialize);
+}
+
+void DynamicLoaderPOSIXDYLD::DebuggerInitialize(Debugger &debugger) {
+  if (!PluginManager::GetSettingForDynamicLoaderPlugin(
+          debugger, PluginProperties::GetSettingName())) {
+    const bool is_global_setting = true;
+    PluginManager::CreateSettingForDynamicLoaderPlugin(
+        debugger, GetGlobalPluginProperties().GetValueProperties(),
+        "Properties for the POSIX dynamic loader plug-in.", is_global_setting);
+  }
 }
 
 void DynamicLoaderPOSIXDYLD::Terminate() {}

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.h

@@ -28,6 +28,8 @@ class DynamicLoaderPOSIXDYLD : public lldb_private::DynamicLoader {
 
   static void Initialize();
 
+  static void DebuggerInitialize(lldb_private::Debugger &debugger);
+
   static void Terminate();
 
   static llvm::StringRef GetPluginNameStatic() { return "posix-dyld"; }

lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLDProperties.td

@@ -0,0 +1,8 @@
+
+include "../../../../include/lldb/Core/PropertiesBase.td"
+
+let Definition = "dynamicloaderposixdyld" in {
+  def ParallelModuleLoad: Property<"parallel-module-load", "Boolean">,
+    DefaultFalse,
+    Desc<"Enable experimental loading of modules in parallel for the POSIX dynamic loader.">;
+}