[Chapel Merge] Use the clang tested with CHPL_LLVM=system and not

Branch: refs/heads/master
Revision: fd323bf
Author: mppf
Log Message:

Merge pull request #17862 from mppf/use-llvm-system-clang-not-38

Use the clang tested with CHPL_LLVM=system and not 3.8

This is to resolve some nightly testing failures with clang 3.8 (which
doesn't really support C++14 in some configurations due to a problem with
GCC headers).

Removes util/cron/test-linux64-clang38.bash in favor of
util/cron/test-linux64-clang.bash which already exists.

Reviewed by @Maxrimus - thanks!

Modified Files:
R util/cron/test-linux64-clang38.bash

M util/cron/test-perf.chapcs.clang.bash

Compare: https://github.com/chapel-lang/chapel/compare/0792e47f872f...fd323bf64137