When generating the `IMPORTED_CXX_MODULES_[CONFIG]` target property,
there was a missing path separator after a non-empty relative directory
part of the path to a module source file.
Co-authored-by: Brad King <brad.king@kitware.com>
The existing `export-interfaces-{build,install}` tests were actually
doing this, but make those test exporting the interfaces and copy the
existing tests to tests which explicitly test the "no properties"
condition.
These patches now support the `-MF` output, so remove the `none` support
added just for the old patchset which did not use it.
Also update the flag name to `-fmodule-output=`.
Due to the new Clang module mapper flag, use a new experimental support
UUID as well.
Ben Boeckel
TylerandBrad King