Where the code of fish was just recently ported over to rust its trying to do lto to fish even though I don't have it set for rust.
Created attachment 922809 [details] emerge --info
Created attachment 922811 [details] build.log for fish
Calling filter-lto before cmake_src_configure fixes it. It looks like cmake_src_configure somehow makes cargo_src_compile use the CFLAGS cmake_src_configure was called with.