[clang] fix oops: enable implicit moves in MSVC compatibility mode

When disabling simpler implicit moves in MSVC compatibility mode as
a workaround in D105518, we forgot to make the opposite change and
enable regular (P1825) implicit moves in the same mode.

As a result, we were not doing any implicit moves at all. OOPS!

This fixes it and adds test for this.

This is a fix to a temporary workaround, there is ongoing
work to replace this, applying the workaround only to
system headers and the ::stl namespace.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D106303