glibc: remove runtime dependency on build-sys bash when cross-compiling

The sotruss tool from the glibc package has a reference to build-sys
bash; its shebang is /bin/sh and the standard builder changes that to
/nix/store/HASH-bash/bin/sh in the fixupPhase.

There is already a list of tools that are removed when cross-compiling
to avoid depending on build-sys bash. Add sotruss to that list.