The gcc compiler can be configured to use `ld.gold` by default. It will
then call `ld.gold` explicitly when linking. When so, spack need to have
a ld.gold wrapper in PATH to inject rpaths link flags etc...
Also I wouldn't be surprised to see some package calling `ld.gold`
directly.
As for ld.gold, the argument could be made that we want to support any
package that could call ld.lld.
