code: def get_c_sources(folder, include_headers=False):
      
      allowed_extensions = [".c", ".C", ".cc", ".cpp", ".cxx", ".c++"]
      if include_headers:
          allowed_extensions += [".h", ".hpp"]
      sources = []
      for root, _, files in os.walk(folder):
          for name in files:
              ext = os.path.splitext(name)[1]
              if name == "types.cc":
                  # Make sure `types.cc` is compiled first, as it has multiple
                  # useful static assertions.
                  sources.insert(0, os.path.join(root, name))
              elif ext in allowed_extensions:
                  sources.append(os.path.join(root, name))
      return sources
docs: Find all C/C++ source files in the `folder` directory.