Option `KokkosTools_REUSE_KOKKOS_COMPILER` does not work

[maartenarnst]

Because the call to project can be expected to already set CMAKE_CXX_COMPILER

• https://github.com/kokkos/kokkos-tools/blob/a9453b21e09c7555096f3a96bb3fa8b34afe19f8/CMakeLists.txt#L3

the option KokkosTools_REUSE_KOKKOS_COMPILER can no longer change CMAKE_CXX_COMPILER

• https://github.com/kokkos/kokkos-tools/blob/a9453b21e09c7555096f3a96bb3fa8b34afe19f8/CMakeLists.txt#L65-L68

so the option KokkosTools_REUSE_KOKKOS_COMPILER can be expected not to work.

Ways forward could be

• remove the option KokkosTools_REUSE_KOKKOS_COMPILER
• use FORCE in the set command

Using FORCE would indeed "reuse" the compiler, but it may not be a good solution because some flags may have been set already in the toolchain for the compiler that is now being overridden with force.

Note that the CMake documentation says that CMAKE_CXX_COMPILER may be set only once:

• https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_COMPILER.html

Joint work with @romintomasetti.