IAU changes dry mass

[jswhit2]

to fix this, implement fixer from GMAO (https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0870.2007.00299.x).

NOAA-EMC/GFDL_atmos_cubed_sphere#14
#58

code from GEOS5 provided by @aerorahul

[jswhit]

This is ready to go now. To test, set iau_drymassfixer=T in &gfs_physics_nml.

Grepping 'mean dry' in the model stdout shows that with iau_drymassfixer=F (the default)

 mean dry surface pressure =    983.0064
 mean dry surface pressure =    983.0065
 mean dry surface pressure =    983.0050
 mean dry surface pressure =    983.0049

and with iau_drymassfixer=T (64 bit executable)

 mean dry surface pressure =    983.0064
 mean dry surface pressure =    983.0064
 mean dry surface pressure =    983.0062
 mean dry surface pressure =    983.0062

[edited to replace results with 64 bit executable with results using a 32 bit executable]

[jswhit2]

https://github.com/jswhit2/ufs-weather-model (branch iau_drymassfixer) has .gitmodules updated to point to the necessary GFDL_atmos_cubed_sphere and fv3atm forks and branches.

[jswhit2]

Fixed by PR #61, ufs-community/ufs-weather-model#56 and NOAA-EMC/GFDL_atmos_cubed_sphere#14