ci: Fix broken link in build-powerpc64le-toolchain.sh

[kennytm]

r? @rust-lang/infra

This is just an emergency fix to keep bors running for another week. I think the numbers will be broken soon. Can we verify if this statement is still true later?

First, download the CentOS7 glibc.ppc64le and relevant header files.
(upstream ppc64le support wasn't added until 2.19, which el7 backported.)

[kennytm]

Or we could cache those files in our S3 again...

[alexcrichton]

@bors: r+ p=100

[bors]

📌 Commit 1f95c6d has been approved by alexcrichton

[bors]

⌛ Testing commit 1f95c6d with merge 525b81d...

[kennytm]

cc @cuviper

[kennytm]

Looks like we could use the URL http://vault.centos.org/altarch/7.3.1611/os/ppc64le/Packages/ as well, if we absolutely want to stay on the same Centos version.

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 525b81d to master...

[cuviper]

@kennytm As long as the basic glibc and kernel versions are the same, our compatibility won't be affected. Bumping to newer package releases shouldn't change ABI at all.

In any case, using a vault link does seem like a better idea for longevity.

Can we verify if this statement is still true later?

I'm not sure what you're asking to verify -- it's just a fact that el7 backported ppc64le support.

[kennytm]

@cuviper I see. I asked because the ppc64 script looks much simpler and doesn't download anything ^^

@alexcrichton So for the backport to beta we'll switch to http://vault.centos.org/altarch/7.3.1611/os/ppc64le/Packages/ instead of reusing this PR. I'll submit another PR for master using the vault link as well?

[cuviper]

Yeah, ppc64(be) has been around much longer and doesn't need special backports, so for that we just use plain upstream versions via crosstool-ng.