Installation complete.
Traceback (most recent call last):
  File "Tools/Scripts/update-webkit-flatpak", line 28, in <module>
    WebkitFlatpak.load_from_args(["--update"] + sys.argv[1:]).run()
  File "./Tools/flatpak/flatpakutils.py", line 866, in run
    return self.main()
  File "./Tools/flatpak/flatpakutils.py", line 858, in main
    toolchains = self.pack_toolchain(("gcc", "g++"), {"/usr/bin/c++": "/usr/bin/g++"})
  File "./Tools/flatpak/flatpakutils.py", line 903, in pack_toolchain
    self.run_in_sandbox(*command, stdout=tmpfile, cwd=self.source_root)
  File "./Tools/flatpak/flatpakutils.py", line 792, in run_in_sandbox
    toolchain_path = self.icc_version[toolchain_name]
KeyError: 'gcc'
Died at Tools/Scripts/update-webkitwpe-libs line 28.