Fix CMake errors on non-english systems (ROOT-8917).
Fix CMake errors on non-english systems (ROOT-8917).

We often parse the output of commands to get certain system
information. This however fails as soon as the system locale changes
which results in cryptic errors where certain variables have the
wrong content on an otherwise perfectly fine working system.

This patch sets LANG=C from CMake to force all subprocesses that
we run to use the stable C locale that should prevent all those
errors in the future.

root-mirror/root,zzxuanyuan/root,olifre/root,olifre/root,olifre/root,zzxuanyuan/root,karies/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root,simonpf/root,olifre/root,karies/root,zzxuanyuan/root,olifre/root,simonpf/root,simonpf/root,zzxuanyuan/root,zzxuanyuan/root,karies/root,karies/root,karies/root,zzxuanyuan/root,zzxuanyuan/root,simonpf/root,root-mirror/root,karies/root,karies/root,karies/root,zzxuanyuan/root,simonpf/root,root-mirror/root,root-mirror/root,simonpf/root,zzxuanyuan/root,olifre/root,karies/root,olifre/root,simonpf/root,karies/root,zzxuanyuan/root,simonpf/root,olifre/root,olifre/root,simonpf/root,zzxuanyuan/root,olifre/root,root-mirror/root,simonpf/root,simonpf/root,root-mirror/root,root-mirror/root,olifre/root,zzxuanyuan/root