fix: add .xlings.json (xmake + musl-gcc + llvm)

Author: Sunrisepeak

.xlings.json

@@ -0,0 +1,7 @@
+{
+  "workspace": {
+    "xmake": "3.0.7",
+    "musl-gcc": { "linux": "15.1.0" },
+    "llvm": { "macosx": "20.1.7" }
+  }
+}