Upgrade libffi for musl builds

[geofft]

We're using a separate, older copy of libffi for musl builds only:

commit 3eb4be5293b4b2c0bb0057a30f14a6379447e4f1
Author: Gregory Szorc <gregory.szorc@gmail.com>
Date:   Thu Jan 18 18:42:15 2024 -0800

    unix: upgrade libffi 3.3 -> 3.4 (except Linux musl)
    
    On Linux musl, we encounter a missing `linux/limits.h` include.
    Possibly from building with ancient Linux headers.

commit 0ecedff54523b9d74cbcb9927e292f034aef4af3
Author: Gregory Szorc <gregory.szorc@gmail.com>
Date:   Thu Jan 18 18:22:32 2024 -0800

    unix: rename libffi -> libffi-3.3
    
    In preparation for introducing libffi 3.4.

We can probably just find a way to get the header?

[indygreg]

I think you should upgrade the Debian version (because it is now 2025). Pulling in the newer kernel sources may make this error go away.