Fix unused-but-set-variable building with GCC

When building with GCC8.1, has error: variable ‘kUpperBoundIsMax’,
‘kLowerBoundIsMin’ set but not used [-Werror=unused-but-set-variable]
so, using USE(var) to fix this error

Change-Id: I05133d3cb5843f4c0a4a59591470b0fcaa21f16f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1848852
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64245}

src/base/macros.h

@@ -388,6 +388,9 @@ bool is_inbounds(float_t v) {
   constexpr bool kUpperBoundIsMax =
       static_cast<biggest_int_t>(kUpperBound) ==
       static_cast<biggest_int_t>(std::numeric_limits<int_t>::max());
+  // Using USE(var) is only a workaround for a GCC 8.1 bug.
+  USE(kLowerBoundIsMin);
+  USE(kUpperBoundIsMax);
   return (kLowerBoundIsMin ? (kLowerBound <= v) : (kLowerBound < v)) &&
          (kUpperBoundIsMax ? (v <= kUpperBound) : (v < kUpperBound));
 }