Make GEOSldas work for SLES15 / Milan

[weiyuan-jiang]

Address issue #691 and added support for SLES15

[biljanaorescanin]

All Nightly Tests passed on SLES-12.
I was able to run few day experiment on SLES-15.
If we wish to run Nightly Tests on SLES-15 some changes are still needed.

[gmao-rreichle]

@biljanaorescanin ran the Nightly Tests on SLES15 and reports only roundoff differences. (The CNCLM45 test fails to run on GNU because of a floating point exception, which is addressed here: GEOS-ESM/GEOSgcm_GridComp#898.)

I further verified that @biljanaorescanin's LDAS_GLOBAL/assim test on SLES-15 has only roundoff differences based on my usual plots of the brightness temperature O-Fs and A-Fs.

[gmao-rreichle]

@GEOS-ESM/cmake-team : Can you please approve this PR or let us know what might need changing? Thanks!

[mathomp4]

@GEOS-ESM/cmake-team : Can you please approve this PR or let us know what might need changing? Thanks!

@gmao-rreichle We can't approve until it is no longer draft. But the Cmake looks fine to me.