libsanitize support in gcc requires features (wordexp.h netrom.h and possibly more) that are not available in uclibc on arm (and possibly other arches). Crossdev should therefore add -sanitize to the package.use/${tuple} that is generated. I am not 100% sure how to correctly integrate this into the crossdev target parsing logic. The attached patch details how I have achieved this for myself.
Created attachment 471766 [details, diff] crossdev_no_sanitize_uclibc-arm.patch
Thanks for the report! Hopefully fixed by USE=sanitize whitelist on glibc-only targets: https://gitweb.gentoo.org/proj/crossdev.git/commit/?id=eedf77d75e5c31e21ec249ba7d4341c32e3ae84f
