Simplify creation of Fortran function wrappers

The old version invoked a Fortran compiler to figure out the bindings necessary to link to a Fortran function. This creates a dependency on having a Fortran compiler, even though the project may not have any Fortran source it needs to compile!

Also, the Fortran compiler that is installed on the system may not be the same as was used to compile the library anyway, so we are not even sure that this is correct!

Furthermore, FindLAPACK operates on the assumption that names in that library is suffixed with a single underscore, so if that is not correct, we won't find any of the functions in that library anyway!

Thus, this patch enables us to assume that appending an underscore is the right thing to do without using the compiler. This option is on by default, since this is the most common case. In case we compile on a
platform where this is *not* the case, we can set the option `USE_FORTRAN_UNDERSCORE=OFF` which will trigger more elaborate detection.

This enables us to build opm-upscaling without having a Fortran compiler installed (and consider that there is no LLVM Fortran compiler for the foreseeable future).