Misc fixes for configure

[matwey]

Currently,
./configure at armv6 machines ends up with

configure: error: unknown CPU type: armv6l

./configure at armv7 machines silently produces build for armv6 (compatible, but suboptimal)

configure: CFG_BUILD := arm-unknown-linux-gnueabihf

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aturon (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[alexcrichton]

Thanks for the PR! Right now rustup has a similar block but also has this:

[alexcrichton]

Er, hit comment too soon, but rustup also has this:

# Detect armv7 but without the CPU features Rust needs in that build,# and fall back to arm.# See https://github.com/rust-lang-nursery/rustup.rs/issues/587.if [ $_ostype="unknown-linux-gnueabihf"-a$_cputype= armv7 ];thenif ensure grep '^Features' /proc/cpuinfo | grep -q -v neon;then# At least one processor does not have NEON.local _cputype=arm
fifi

I wonder if that also needs to be included here? Could you also elaborate on the purpose of the PR in the description as well?

cc @brson

[matwey]

@alexcrichton I am not sure that your code snippet is necessary.

[alexcrichton]

Ah I erroneously thought that the armv7 Linux target enabled NEON, which we needed to specifically check for lack of support and go back to arm. Due to a recent PR, though, we no longer assume NEON on armv7, so this is fine.

@bors: r+

[bors]

📌 Commit 9b81f3c has been approved by alexcrichton