We're going to remove the support for modules-ts. But there are a lot of
tests which uses -fmodules-ts. We shouldn't remove them simply. This
patch refactor these tests to use standard c++ modules.
This switches from the prototype syntax in P0273R0 ('module' and 'module
implementation') to the consensus syntax 'export module' and 'module'.
In passing, drop the "module declaration must be first" enforcement, since EWG
seems to have changed its mind on that.
llvm-svn: 301056
