Switch dynamic musl cross compilation to using an `abilists` file

[alexrp]

The current libc.S is fairly big by virtue of being text, and does not allow tracking the musl version that a symbol was introduced in. We should just switch to an abilists file via libc-abi-tools.

When doing this, we should collect symbol lists going back to musl 1.2.0 if possible.

[alexrp]

An abilists file covering 1.2.0 through 1.2.5 is 37 KB compared to libc.S which is 101 KB and only covers the latest version of musl.