[4.0] Rename 'PluginConfig' struct to fix lto warnings

[naithar]

Should cover C++ One Definition Rule warning for PluginConfig struct from: #45179

Added a prefixes for platform's PluginConfig struct and plugin constants to remove possible name collisions.

This changes are already cherry-picked for #41340

[akien-mga]

Maybe those should be class constants so that they're properly namespaced? Then we don't need the suffix.

[akien-mga]

I think we'd typically use PluginConfigAndroid to further specify PluginConfig (see EditorExportPlatformAndroid).

Which raises the question of whether this shouldn't be made abstract as a PlatformPluginConfig interface that each platform can implement, when relevant? Though that's outside the scope of this PR.

[naithar]

@akien-mga fixed some of your comments, should be fine now.
Not sure about shared PlatformPluginConfig interface. Maybe we can implement it once more platforms support plugins, but for now I don't think it would give any benefit.

[akien-mga]

You should be able to have the values declared inline with C++11 no?

[naithar]

No, got inline initializer error on compilation, so left it as it is now.

[akien-mga]

According to https://stackoverflow.com/a/1563906 this may work with inline in C++17 (which we use).

[akien-mga]

Confirmed that it builds fine (with GCC at least):

diff --git a/platform/android/plugin/godot_plugin_config.h b/platform/android/plugin/godot_plugin_config.h
index 04091b49f7..a2ea42d311 100644
--- a/platform/android/plugin/godot_plugin_config.h
+++ b/platform/android/plugin/godot_plugin_config.h
@@ -51,7 +51,7 @@ The `dependencies` section and fields are optional and defined as follow:
  See https://github.com/godotengine/godot/issues/38157#issuecomment-618773871
  */
 struct PluginConfigAndroid {
-       static const char *PLUGIN_CONFIG_EXT;
+       inline static const char *PLUGIN_CONFIG_EXT = ".gdap";
 
        static const char *CONFIG_SECTION;
        static const char *CONFIG_NAME_KEY;
@@ -84,8 +84,6 @@ struct PluginConfigAndroid {
        Vector<String> custom_maven_repos;
 };
 
-const char *PluginConfigAndroid::PLUGIN_CONFIG_EXT = ".gdap";
-
 const char *PluginConfigAndroid::CONFIG_SECTION = "config";
 const char *PluginConfigAndroid::CONFIG_NAME_KEY = "name";
 const char *PluginConfigAndroid::CONFIG_BINARY_TYPE_KEY = "binary_type";

[naithar]

Fixed. Not sure if 3.2 should get an inline change as it gives: warning: inline variables are a C++17 extension [-Wc++17-extensions]

[akien-mga]

Thanks!

Not sure if 3.2 should get an inline change as it gives: warning: inline variables are a C++17 extension [-Wc++17-extensions]

Indeed the 3.2 codebase is compiled with C++14 (while the code is mostly C++03 with some C++11 features, but we don't make any extensive use of new features there). So you might have to keep the non-inline version there.