CESM exact restart test fails with gnu

[alperaltuntas]

The exact restart test (ERS) fails when MOM6 gets compiled with gnu in CESM. This issue occurs with gnu but not with intel because of a difference in the implementation of inquire intrinsic. Take the following program:

program foo
  logical :: fexists
  inquire(file='./', exist=fexists)
  print *, fexists
end program

When compiled with gnu, the program prints out T, whereas when compiled with intel, the program prints out F. Simply, gnu (correctly) says that ./ exists, whereas intel says that ./ doesn't exist. This behavioral difference manifests itself in MOM_restart::open_restart_units subroutine. If the restart directory is "./" and filename begins with a whitespace, gnu incorrectly concludes that the filepath for the first* restart file is filepath="./", whereas intel is eventually able to get the correct filepath, since it (incorrectly) knows that ./ doesn't exist. I will implement a correction in the logic of the subroutine and submit a PR once all tests pass.

*there may be multiple restart files in the single character string passed to open_restart_units , and the subroutine gets each restart filename in a do while loop by checking if it encounters a whitespace in between filenames.