(*)Parenthesize tracer_advect PPM edge values

  Added parentheses to 4 tracer edge value calculations used with PPM tracer
advection to give rotationally consistent solutions when fused-multiply-adds are
enabled.  Although these lines may not appear to need parentheses, some
compliers appear to be putting these expressions directly into others, where the
direction of the flow seems to determine which multiplications are incorporated
into FMAs.  All answers are bitwise identical in cases without FMAs, but answers
could change when FMAs are enabled.

src/tracer/MOM_tracer_advect.F90

@@ -537,9 +537,9 @@ subroutine advect_x(Tr, hprev, uhr, uh_neglect, OBC, domore_u, ntr, Idt, &
         if (G%mask2dCu(I_up,j)*G%mask2dCu(I_up-1,j)*(Tp-Tc)*(Tc-Tm) <= 0.) then
           aL = Tc ; aR = Tc ! PCM for local extrema and boundary cells
         elseif ( dA*(Tc-mA) > (dA*dA)/6. ) then
-          aL = 3.*Tc - 2.*aR
+          aL = (3.*Tc) - 2.*aR
         elseif ( dA*(Tc-mA) < - (dA*dA)/6. ) then
-          aR = 3.*Tc - 2.*aL
+          aR = (3.*Tc) - 2.*aL
         endif
 
         a6 = 6.*Tc - 3. * (aR + aL) ! Curvature
@@ -922,9 +922,9 @@ subroutine advect_y(Tr, hprev, vhr, vh_neglect, OBC, domore_v, ntr, Idt, &
         if (G%mask2dCv(i,J_up)*G%mask2dCv(i,J_up-1)*(Tp-Tc)*(Tc-Tm) <= 0.) then
           aL = Tc ; aR = Tc ! PCM for local extrema and boundary cells
         elseif ( dA*(Tc-mA) > (dA*dA)/6. ) then
-          aL = 3.*Tc - 2.*aR
+          aL = (3.*Tc) - 2.*aR
         elseif ( dA*(Tc-mA) < - (dA*dA)/6. ) then
-          aR = 3.*Tc - 2.*aL
+          aR = (3.*Tc) - 2.*aL
         endif
 
         a6 = 6.*Tc - 3. * (aR + aL) ! Curvature