Arch Linux

As specified in the RFC[1] we need to check packages that make use of `malloc_usable_size`:

> Some applications use malloc_usable_size (despite the glibc manual stating it is for diagnostic purposes only). This is currently incompatible with _FORTIFY_SOURCE=3, so these packages will need to continue using level 2 by modifying C{,XX}FLAGS in the PKGBUILD. A TODO list will be created for all such packages on adoption of this proposal.

This list was generated using a scanner[2] that runs `readelf -Ws <path>` on all ELF binaries and checks the output for mentions of `malloc_usable_size@GLIBC`.

A possible fix looks like this:
```
# this uses malloc_usable_size, which is incompatible with fortification level 3
export CFLAGS="${CFLAGS/_FORTIFY_SOURCE=3/_FORTIFY_SOURCE=2}"
export CXXFLAGS="${CXXFLAGS/_FORTIFY_SOURCE=3/_FORTIFY_SOURCE=2}"
```

[1]: https://gitlab.tyrtyr.thefun.eu.org/archlinux/rfcs/-/blob/master/rfcs/0017-increase-fortification-level.rst
[2]: https://github.com/kpcyrd/archlinux-scan-malloc-usable-size
[3]: https://gitlab.tyrtyr.thefun.eu.org/archlinux/devtools/-/merge_requests/191