libisl.so.23 is used by gcc12, it does not exist in gcc12 Makefile.
Could you please provide more details? I see LIB_DEPENDS+= libisl.so:devel/isl on line 143, which is added only if the GRAPHITE option is on, consistent with what I read in https://gcc.gnu.org/wiki/InstallingGCC . Do you mean that gcc12 is linked with libisl.so even if the option is OFF if devel/isl is installed? Could you please provide some steps to reproduce what you observe? Also please note that I am in the middle of a difficult update of GCC default version from 12 to 13 (and also in the middle of many other things), so I might need some time to address this bug report. Thanks.
(In reply to Lorenzo Salvadore from comment #1) GRAPHITE is off, but it links with lib.