Merge branch 'singhbalwinder/sea-ice/fix-threading-bug-maint2' into maint-2.0 (PR #5063)

Adds omp critical directives for ice warnings (for maint2.0)

While running some ensemble members for v2 on Cori-KNL, we occasionally
hit errors like "forrtl: severe (151): allocatable array is already
allocated" pointing to ice_warnings.f90 file. Adding an "omp critical"
section in this file fixes these errors.

[BFB]

Author: jonbob

components/mpas-seaice/src/column/ice_warnings.F90

@@ -42,7 +42,7 @@ subroutine add_warning(warning)
     integer :: &
          nWarningsArray, & ! size of warnings array at start
          iWarning ! warning index
-
+    !$omp critical (ice_warnings_add_warning_critical)
     ! check if warnings array is not allocated
     if (.not. allocated(warnings)) then
 
@@ -90,7 +90,7 @@ subroutine add_warning(warning)
 
     ! add the new warning
     warnings(nWarnings) = trim(warning)
-
+    !$omp end critical (ice_warnings_add_warning_critical)
   end subroutine add_warning
 
 !=======================================================================