Add package.env that passes user-defined-trusted-dirs to glibc

[bedroge]

Now we just need to make sure that it's actually used, as the bootstrap will not make use of this. So I guess we should add glibc to our set to make sure it gets reinstalled?

Closes #7.

[ocaisa]

Some interesting comments on this in easybuilders/easybuild-easyconfigs#5329

Note trusted here comes from the fact they are considered by suid binaries too, which ignore LD_LIBRARY_PATH. Such default dirs are also then considered for indirect library dependencies, like RPATH but unlike RUNPATH

and this one about using patchelf on our binary installations is also interesting: https://stackoverflow.com/a/44710599
@boegel is that something that we could get EB to handle or should we consider a hook or something?