sysroot_linux-64 upgrade (and syntax error?)

[KrisThielemans]

The line seems to require 2.17 (but there seems to be a missing = or >=)

root-feedstock/recipe/meta.yaml

Line 64 in f157c9f

- sysroot_linux-64 2.17 # [linux]

However, 2.17 has a problem when linking to libpthread.so. More information is on conda-forge/stir-feedstock#101 (comment). Upgrading to a more recent sysroot (i.e. glibc) seeems to resolve this. I've only checked with 2.28