Revert of ensure host compiler is always clang when cross compiling from linux (patchset #6 id:100001 of https://codereview.chromium.org/955393002/)

Reason for revert:
broke some things

Original issue's description:
> ensure host compiler is always clang when cross compiling from linux
>
> BUG=
>
> Committed: https://crrev.com/56039af476797accc238dcb24c7ab926899287a0
> Cr-Commit-Position: refs/heads/master@{#26881}

TBR=machenbach@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/964483002

Cr-Commit-Position: refs/heads/master@{#26882}