Rollup merge of #143415 - Gelbpunkt:cleanup-dist-ppc64le-toolchain, r=marcoieni

Get rid of build-powerpc64le-toolchain.sh

The dist-powerpc64le-linux-musl runner never actually used the toolchain that the script produced, it instead used the one from crosstool-ng.

The dist-powerpc64le-linux-gnu runner did use it, from what I can tell mainly to get a glibc 2.17 version with ppc64le support backported. Since crosstool-ng has the necessary patches, we can just use crosstool-ng to get an appropriate toolchain. While at it, use kernel 3.10 headers since that's the version documented in platform support for this target.

try-job: dist-powerpc64le-linux-gnu
try-job: dist-powerpc64le-linux-musl

Author: jieyouxu