Symmetry: Use and adapt to custom dub with inheritable dub.selections…

….json support

See https://github.com/symmetryinvestments/dub/commits/sym-1.37.x/,
also including an important tweak for LDC related to symbol visibility
on Windows.

dub.selections.json

@@ -1,7 +1,7 @@
 {
 	"fileVersion": 1,
 	"versions": {
-		"dub": "1.36.0",
+		"dub": {"repository":"git+https://github.com/symmetryinvestments/dub.git","version":"f4e32c8c4c470fd3b17369752edf93922d0db90e"},
 		"unit-threaded": "2.1.7"
 	}
 }

payload/reggae/options.d

@@ -232,8 +232,18 @@ struct Options {
             maybeDubDeps ~= _dubProjectFile;
 
             const selectionsJsonPath = buildPath(projectPath, "dub.selections.json");
-            if (selectionsJsonPath.exists)
+            if (selectionsJsonPath.exists) {
                 maybeDubDeps ~= selectionsJsonPath;
+            } else version(Have_dub) {
+                import dub.project: lookupAndParseSelectionsFile;
+                import dub.internal.vibecompat.inet.path: NativePath;
+
+                () @trusted {
+                    const res = lookupAndParseSelectionsFile(NativePath(projectPath));
+                    if (!res.isNull())
+                        maybeDubDeps ~= res.get().absolutePath.toNativeString();
+                }();
+            }
         }
 
         return ranFromPath ~ maybeReggaeFile ~ maybeReggaeFileDeps ~ maybeDubDeps ~ dependencies;