Fix superlu version variable in cmake config
Small bugfix / issue. Seems the SUPERLU_MAJOR_VERSION was not escaped correctly in RatCommonConfig. Created issues when using find_package(RatCommon) in the other libraries. I also added output to be more clear if superlu is being enabled.
Additionally this SUPERLU_MAJOR_VERSION variable is not being set by find_package(superlu) on my end so I have resorted to sending it on the command line through -DSUPER_MAJOR_VERSION=5. Not sure if this is intended behavior. Using superlu 5.2.2 if that matters.
Best