(*)Parenthesize tracer_hordiff for FMAs

  Added parentheses to the calculation of the diffusive temperature changes in
tracer_hordiff so that it will be rotationally invariant when
fused-multiply-adds are enabled.  All answers are bitwise identical in cases
without FMAs, but answers could change with FMAs.

src/tracer/MOM_tracer_hor_diff.F90

@@ -546,10 +546,10 @@ subroutine tracer_hordiff(h, dt, MEKE, VarMix, visc, G, GV, US, CS, Reg, tv, do_
         do m=1,ntr
           do j=js,je ; do i=is,ie
             dTr(i,j) = Ihdxdy(i,j) * &
-              ((Coef_x(I-1,j,1) * (Reg%Tr(m)%t(i-1,j,k) - Reg%Tr(m)%t(i,j,k)) - &
-                Coef_x(I,j,1) * (Reg%Tr(m)%t(i,j,k) - Reg%Tr(m)%t(i+1,j,k))) + &
-               (Coef_y(i,J-1,1) * (Reg%Tr(m)%t(i,j-1,k) - Reg%Tr(m)%t(i,j,k)) - &
-                Coef_y(i,J,1) * (Reg%Tr(m)%t(i,j,k) - Reg%Tr(m)%t(i,j+1,k))))
+              ( ((Coef_x(I-1,j,1) * (Reg%Tr(m)%t(i-1,j,k) - Reg%Tr(m)%t(i,j,k))) - &
+                 (Coef_x(I,j,1) * (Reg%Tr(m)%t(i,j,k) - Reg%Tr(m)%t(i+1,j,k)))) + &
+                ((Coef_y(i,J-1,1) * (Reg%Tr(m)%t(i,j-1,k) - Reg%Tr(m)%t(i,j,k))) - &
+                 (Coef_y(i,J,1) * (Reg%Tr(m)%t(i,j,k) - Reg%Tr(m)%t(i,j+1,k)))) )
           enddo ; enddo
           if (associated(Reg%Tr(m)%df_x)) then ; do j=js,je ; do I=G%IscB,G%IecB
             Reg%Tr(m)%df_x(I,j,k) = Reg%Tr(m)%df_x(I,j,k) + Coef_x(I,j,1) &