This ticket is to replace BACKPORT-16506 which is porting WT-11239 to the 6.0 branch. The fix is still required, but evergreen.yml has had enough changes between 7.0 and 6.0 that the original fix no longer applies.

This ticket addressed the FIXME-WT-11239 comments by re-enablng the compile-clang variants and updates their configurations to make sure older versions of clang (7.0, 8.0) are using the correct toolchains to compile.