benchmarks: fix some (future) -Wunused-result warnings

Clang 10 warns about unused results of relational operators, which is
where this is coming from.

Fix by adding the usual prefix

  [[maybe_unused]] auto r = ~~~;

to silence the warning. Do this elsewhere, too, since [[nodiscard]] is
slowly being rolled out across all our APIs. This is not a complete
sweep, though.

Not picking to 5.15, because this pattern doesn't work there and I
don't want to introduce a new one.

Pick-to: 6.3 6.2
Change-Id: I40dd8ad07496b686979dce533e044cbb486e30f3
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

0 files changed, 0 insertions, 0 deletions