Bootstrap build of Portola on Alpine

[Josh Graham]

G'day Mikael,

Out of curiosity, why did you have to do the poll.h softlink workaround? I
> was naively hoping I had fixed all of the incorrect includes, but maybe I
> missed something?
>

With warnings-as-errors the content of `sys/poll.h` emits a warning, thus
raises an error. I suppose that flag could be turned off. There's a few
-Xlint warnings, too, which may warrant further investigation.



> bash ./configure --host=x86_64-unknown-linux-musl
> --build=x86_64-unknown-linux-musl <…>
>

Trying that now (along with a `make clean`). The new `--openjdk-target`
argument looks interesting, I'll play with that too at some point.

After I get a good build, I'll iterate from fresh and incorporate the `sed`
idea and fewer package installs. Then it's on to runtime testing!

Cheers,
Josh