[libc++] Add a CI configuration to test Modules with LSV enabled

[libc++] Add a CI configuration to test Modules with LSV enabled

Some clients use libc++ with modules and LSV (Local Submodule Visibility)
enabled, and we see frequent downstream breakage caused by that. Until
modules use LSV by default (which is apparently a desire), add a CI job
that tests this sub-configuration to avoid high cost downstream breakage.

For more information about LSV, see https://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20150504/128395.html.

Differential Revision: https://reviews.llvm.org/D143273