Replace Boost.Dll with our own function

Now we no longer rely on anything from Boost. Later we'll move the path
detection to the very beginning of the plugin bridge initialization so
it can be set from the coming chainloader libraries.

src/common/linking.h

@@ -0,0 +1,32 @@
+// yabridge: a Wine VST 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
+
+// This header is completely standalone so the chainloading libraries can
+// retrieve their file path without pulling in a lot of additional dependencies
+
+#include <string>
+
+/**
+ * Return a path to this `.so` file. This can be used to find out from where
+ * this copy of `libyabridge-{vst2,vst3}.so` or `libyabridge-chainloader-*.so`
+ * was loaded so we can search for a matching Windows plugin library. When the
+ * chainloaders are used, this path should be passed to the chainloaded plugin
+ * library using the provided exported functions since they can't detect the
+ * path themselves.
+ */
+std::string get_this_file_location();