Find the correct library file from the chainloader

Instead of using this hardcdoed path.

src/chainloader/utils.h

@@ -0,0 +1,37 @@
+// yabridge: a Wine plugin bridge
+// Copyright (C) 2020-2022 Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include <string>
+
+/**
+ * Finds the matching `libyabridge-*.so` for this chainloader. Returns the
+ * handle if it is found. Otherwise, we'll log an error and show a desktop
+ * notification, and this function returns a null pointer. The pointer may be
+ * `dlclose()`'d when it's no longer needed. This search works in the following
+ * order:
+ *
+ * - First we'll try to locate `yabridge-host.exe` using the same method used by
+ *   the yabridge plugin bridges themselves. We'll search in `$PATH`, followed
+ *   by `${XDG_DATA_HOME:-$HOME/.local/share}/yabridge`. If that file exists and
+ *   the target plugin library exists right next to it, then we'll use that.
+ * - For compatibility with 32-bit only builds of yabridge, we'll repeat this
+ *   process for `yabridge-host-32.exe`.
+ * - When those don't exist, we'll try to `dlopen()` the file directly. This
+ *   will use the correct path for the system.
+ */
+void* find_plugin_library(const std::string& name);