added several larger tests in CI. Still missing for gfortran (no
gfortran+cuda tests at the moment, will be added)

- execvp needs the programs name also as first argument in the argument
  list
- len(files) == 1 (i.e. the normal case) was omitted in the last second
  when the error handling was improved

For some reason, and only in certain cases, the built-in
preprocessor of ifort cannot handle constructs such as

  #define FOO bar

  print *, "foo&
  &FOO&
  &baz"

or more specifically

  #define DATATYPE double

  print *, some_&
  &DATATYPE&
  &_routine

which, however, are quite handy. GCC seems to handle those as
expected.

It could happen that ELPA stopped with an error but an exit code "0"
was given, i.e. one could assume everything was fine when it was not!
Now each Fortran "stop" was replaced with "stop 1" to prevent this

This gives a speed-up of up to a factor 2 in the complex version