Fix mosaic2 tests with strict debug flags

This fixes two issues that occur in the `mosaic2` tests when FMS is built using
strict debug flags:

1) The `area` argument of `calc_mosaic_grid_area` has been changed from
`intent(inout)` to `intent(out)`, to avoid an uninitialized value error.

2) `atan` has been changed to `atan2` in the unit tests, to avoid
divide-by-zero errors.

mosaic2/include/mosaic2.inc

@@ -86,15 +86,13 @@
   !> <br>Example usage:
   !!            call calc_mosaic_grid_area(lon, lat, area)
   subroutine CALC_MOSAIC_GRID_AREA_(lon, lat, area)
-     real(kind=FMS_MOS_KIND_), dimension(:,:), intent(in)    :: lon
-     real(kind=FMS_MOS_KIND_), dimension(:,:), intent(in)    :: lat
-     real(kind=FMS_MOS_KIND_), dimension(:,:), intent(inout) :: area
+     real(kind=FMS_MOS_KIND_), dimension(:,:), intent(in)  :: lon
+     real(kind=FMS_MOS_KIND_), dimension(:,:), intent(in)  :: lat
+     real(kind=FMS_MOS_KIND_), dimension(:,:), intent(out) :: area
      integer :: nlon, nlat
 
      real(r8_kind) :: area_r8(size(area,1),size(area,2))
 
-     area_r8=real(area,r8_kind)
-
      nlon = size(area,1)
      nlat = size(area,2)
      ! make sure size of lon, lat and area are consitency

test_fms/mosaic2/test_mosaic2.F90

@@ -254,7 +254,7 @@ subroutine test_is_inside_polygon
   z2(1)=2.0_lkind ; z2(2)=4.0_lkind ; z2(3)=4.0_lkind ; z2(4)=2.0_lkind ; z2(5)=2.0_lkind
   do i=1, n
      r = sqrt( x2(i)**2 + y2(i)**2 + z2(i)**2 )
-     lon2(i)=atan(y2(i)/x2(i))
+     lon2(i)=atan2(y2(i), x2(i))
      lat2(i)=asin(z2(i)/r)
   end do
 
@@ -263,7 +263,7 @@ subroutine test_is_inside_polygon
   y1=5.0_lkind
   z1=4.2_lkind
   r = sqrt(x1**2+y1**2+z1**2)
-  lon1=atan(y1/x1)
+  lon1=atan2(y1, x1)
   lat1=asin(z1/r)
 
   answer=.false.
@@ -275,7 +275,7 @@ subroutine test_is_inside_polygon
   y1=3.0_lkind
   z1=2.5_lkind
   r = sqrt(x1**2+y1**2+z1**2)
-  lon1=atan(y1/x1)
+  lon1=atan2(y1, x1)
   lat1=asin(z1/r)
 
   answer=.true.