|| ( >=sys-devel/gcc-3.3:=[objc] sys-devel/clang ) := operator is forbidden and broken inside || (). I understand what you're trying to do here but since active gcc changes break it anyway, I guess you can drop := and forget about any sanity.
commit 0274bedd5ed2a2723534adbc2859d6e97a2bd9d9 Author: Michał Górny <mgorny@gentoo.org> AuthorDate: Tue Jun 21 22:11:17 2016 Commit: Michał Górny <mgorny@gentoo.org> CommitDate: Tue Jun 21 22:11:33 2016 gnustep-base/gnustep-make: Remove := slot op from || dep, #561728 Leaving the bug open in case you want to restore := support in some way.
Indeed, it could only help a bit in simple cases, but did not help when toying with the active compiler. There are other checks later in the ebuild to try and mitigate these problems, and gnustep-updater can fix most of these. Thanks for the fix, and good bye := in || ()