[FL-2052] New build system based on scons (#1269)

site_scons/site_tools/python3.py

@@ -0,0 +1,13 @@
+def generate(env):
+    py_name = "python3"
+    if env["PLATFORM"] == "win32":
+        # On Windows, Python 3 executable is usually just "python"
+        py_name = "python"
+
+    env.SetDefault(
+        PYTHON3=py_name,
+    )
+
+
+def exists(env):
+    return True