Import source to librtti

Summary:

- Import initial source

Test Plan:
NA

nixSupport/default.nix

@@ -0,0 +1,20 @@
+{
+  pkgs,
+  ...
+}:
+let
+  librtti = pkgs.callPackage ./librtti.nix {
+    inherit pkgs;
+    withDebug = false;
+    withAsan = false;
+  };
+  librtti_debug = pkgs.callPackage ./librtti.nix {
+    inherit pkgs;
+    withDebug = true;
+    withAsan = true;
+  };
+in
+{
+  librtti = librtti;
+  librtti_debug = librtti_debug;
+}