[Math] Replace add_subdirectory by ROOT_ADD_TEST_SUBDIRECTORY.
[Math] Replace add_subdirectory by ROOT_ADD_TEST_SUBDIRECTORY.

The tests for TFoam ended up in the wrong location, since
add_subdirectory is not setting the required property.

karies/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,karies/root,olifre/root,olifre/root,karies/root,karies/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,karies/root,root-mirror/root,olifre/root,olifre/root,olifre/root,olifre/root,root-mirror/root,karies/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,karies/root,karies/root,root-mirror/root