Add subdirectories to source file collection logic in SConstruct using os.walk

Added automatic file collection using os.walk so that source files in subdirectories of src/ get properly detected by SConstruct.

Author: Chkoupinator

SConstruct

@@ -38,7 +38,11 @@ Run the following command to download godot-cpp:
 env = SConscript("godot-cpp/SConstruct", {"env": env, "customs": customs})
 
 env.Append(CPPPATH=["src/"])
-sources = Glob("src/*.cpp")
+sources = []
+for root, folders, files in os.walk("src"):
+    if root.endswith("gen"):
+        continue
+    sources += Glob(os.path.join(root, "*.cpp"))
 
 if env["target"] in ["editor", "template_debug"]:
     try: