proposal: remove partial 32bit support

[lmb]

We don't have a way of testing 32bit support (not available on Semaphore) and it's probably not really used anyway. I think we should remove it.

Thoughts @nathanjsweet ?

[nathanjsweet]

My one concern is ARM. I could see BPF being useful in mobile, but the lack of testing is disconcerting. I say we kill 32 bit for now, and if anybody comes in and has a burning desire to resurrect I'll make sure to support them.

[ti-mo]

No burning desire here, but I have a RPi1 B+ that I'd like to try and run BPF code on. Haven't been able to get anything to run so far, and I'm starting to wonder if C code (written against the kernel) can even be compiled for arm6, since I don't see their registers defined in https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/bpf_helpers.h.