FMS API: Convert real kind of constants

Two latent heat constants are imported directly from FMS, which is built
independently of MOM6.  Previously, it was a safe assumption that both
would be built with double precision, but this is no longer the case
since FMS now supports both single and double precision.  This could
cause conflicts with mixed-precision builds.

This patch converts the values from FMS-precision to MOM-precision.

Single->double should not affect reproducibility since every
single-precision number can be exactly represented in double precision.
Double->single could affect reproducibility, but this is not an issue
since MOM6 does not run in single precision.

config_src/infra/FMS1/MOM_constants.F90

@@ -3,12 +3,16 @@ module MOM_constants
 
 ! This file is part of MOM6. See LICENSE.md for the license.
 
-use constants_mod, only : HLV, HLF
+use constants_mod, only : FMS_HLV => HLV
+use constants_mod, only : FMS_HLF => HLF
 
 implicit none ; private
 
-!> The constant offset for converting temperatures in Kelvin to Celsius
 real, public, parameter :: CELSIUS_KELVIN_OFFSET = 273.15
-public :: HLV, HLF
+  !< The constant offset for converting temperatures in Kelvin to Celsius [K]
+real, public, parameter :: HLV = real(FMS_HLV, kind=kind(1.0))
+  !< Latent heat of vaporization [J kg-1]
+real, public, parameter :: HLF = real(FMS_HLF, kind=kind(1.0))
+  !< Latent heat of fusion [J kg-1]
 
 end module MOM_constants

config_src/infra/FMS2/MOM_constants.F90

@@ -3,12 +3,16 @@ module MOM_constants
 
 ! This file is part of MOM6. See LICENSE.md for the license.
 
-use constants_mod, only : HLV, HLF
+use constants_mod, only : FMS_HLV => HLV
+use constants_mod, only : FMS_HLF => HLF
 
 implicit none ; private
 
-!> The constant offset for converting temperatures in Kelvin to Celsius
 real, public, parameter :: CELSIUS_KELVIN_OFFSET = 273.15
-public :: HLV, HLF
+  !< The constant offset for converting temperatures in Kelvin to Celsius [K]
+real, public, parameter :: HLV = real(FMS_HLV, kind=kind(1.0))
+  !< Latent heat of vaporization [J kg-1]
+real, public, parameter :: HLF = real(FMS_HLF, kind=kind(1.0))
+  !< Latent heat of fusion [J kg-1]
 
 end module MOM_constants