Fix type mismatch error on s390

On s390, size_t is defined to be long unsigned int, while Address is unsigned
int. Therefore, GCC is complaining conflicting types for parameter 'T'
('long unsigned int' and 'unsigned int') for the Min function.

R=ofrobots@google.com, hpayer@chromium.org, mstarzinger@chromium.org, mlippautz@chromium.org

Change-Id: Ib04edebad24da694ccd06ff572ee50d3db7f87ff
Reviewed-on: https://chromium-review.googlesource.com/1035542Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#52900}

src/heap/spaces.cc

@@ -1751,7 +1751,7 @@ Address SpaceWithLinearArea::ComputeLimit(Address start, Address end,
     } else {
       rounded_step = RoundSizeDownToObjectAlignment(static_cast<int>(step));
     }
-    return Min(start + min_size + rounded_step, end);
+    return Min(static_cast<Address>(start + min_size + rounded_step), end);
   } else {
     // The entire node can be used as the linear allocation area.
     return end;