ODR issues with SYCL

[smithsg84]

There are ODR issue when two libraries use RAJA, one with SYCL enabled and one without.

The #ifdef code logic in launchcore methods result in two definitions being created.

https://github.com/LLNL/RAJA/blob/75990d83c72317ade5017464cd04b9b9990ea786/include/RAJA/pattern/launch/launch_core.hpp#L189

A possible solution discussed in #1974 would be to use forced inlining of the methods with the #ifdef logic.

There are some macros to force inlining for various compilers in here:

https://github.com/LLNL/RAJA/blob/develop/include/RAJA/config.hpp.in#L411

[rhornung67]

IMO, any reasonable application build would have one library build and install of RAJA that all parts of the app would use. This is one reason we use Spack to build our stacks.

So, we should keep track of things like this, but I don't think they will cause problems in the real world.