The Source/ThirdParty/ANGLE/gni-to-cmake.py script doesn't currently handle GN's pkg_config and declare_args statements. They don't need to be fully parsed; simply removing them will eliminate some of the manual fixups needed during each ANGLE roll.
Created attachment 455999 [details] Patch
Note that there are important steps to take when updating ANGLE. See https://trac.webkit.org/wiki/UpdatingANGLE
Committed r292053 (248990@main): <https://commits.webkit.org/248990@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 455999 [details].
<rdar://problem/90997571>