Hello Guix,

I'm running Guix on an aarch64 system that uses a Linux kernel configured with
a page size of 16K. Some of the substitutes I receive from Guix sometimes do
not work. I believe all packages that use jemalloc, which are quite a lot.

Rust is one example. It fails like this:

```
[roman@bombaclaat guix]$ rustc
<jemalloc>: Unsupported system page size
<jemalloc>: Unsupported system page size
<jemalloc>: Unsupported system page size
terminate called without an active exception
Aborted
```

Building packages that depend on jemalloc also fail. I can't compile the rust
package from Guix for example.

This patch series updates jemalloc and enables the use of transparent huge
pages on the aarch64 architecture. I saw we support THP as well for i686-linux
and x86_64-linux, so I think it's fine to enable it here as well. At least
it's better than crashing.

The patch should also make it possible to use substitutes built on CI by
systems running with larger kernel pages sizes, avoiding long compilation
times for things like the whole rust toolchain.

Since jemalloc has a lot of dependencies, I think it's a candidate for
core-updates.

I submitted parts of this patch series in another ticket where I tried to fix
Icecat compilation on my aarch64 system. But I think it's worth a separate
issue. And I'm blocked on the other issue at the moment.

Could you please review the patchs?

Thanks, Roman.