Revert "[cling] modulemap <string_view> requires C++17."
Revert "[cling] modulemap <string_view> requires C++17."

This reverts commit 93c1649bef398ee310b85848bbe4a2f0182c3a76.

root-mirror/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling,root-mirror/cling