`makeOverriddable` doesn't work for bundled sbclWith as is because it
uses the `//` operator internally which doesn't work with the types
`bundled` and `sbclWith` accept as arguments (string and list
respectively).
What's more, `bundled` already uses `makeOverridable` and allows to
override the internal call to `library` via `overrideLisp`. For
`sbclWith` no such mechanism exists, but this seems to be no concern for
now: Using `overrideLisp` for this hasn't worked so far (and failed with
a _hideous_ evaluation error), so there doesn't seem to be any real
demand for this feature. Maybe a feature for another CL.
Change-Id: I0b2f34c00a2143cd66dd43a6b1b2880af997ee50
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3296
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>