This variable define how the link step is done. Possible values are:
* DRIVER: the compiler is used as driver for the link step
* LINKER: the linker is used directly for the link step.
This was added in commit 98d0f918ba (LFortran: Add support for this
compiler, 2024-01-25, v3.31.0-rc1~303^2~2) because it is needed for
cases covered by CMake's Fortran tests. However, it does not work
with Fortran modules and breaks lfortran's own `examples/project1`.
Move the flag to the test cases that need it, just as the original
commit did with `--implicit-interface`.
Fixes: #26597
Co-authored-by: Brad King <brad.king@kitware.com>
