When doing a system update after a long time, a problem occurs that some programs, such as dev-libs/libical, net-libs/libproxy and sys-auth/polkit cannot be compiled when a outdated version of dev-libs/gobject-introspection is installed. This problem goes away when manually updating this package (which is already in the update queue). I suggest giving this package a greater priority in the update, if possible, when packages like these are to be emerged, or put a note on these packages informing the user of this problem.
I'm afraid this really needs a build.log (and ideally emerge --info) of the failures to analyse.
I suspect https://bugs.gentoo.org/947058#c1 is what's happening for you.