benchmark

Support -Wsuggest-override (#1059)

* Support -Wsuggest-override

google/benchmark is C++11 compatible but doesn't use the `override` keyword.
Projects using google/benchmark with enabled `-Wsuggest-override` and `-Werror` will fail to compile.

* Add -Wsuggest-override cxx flag

* Revert unrelated formatting

* Revert unrelated formatting, take 2

* Revert unrelated formatting, take 3

* Disable -Wsuggest-override when compiling tests, gtest does not handle it yet

Co-authored-by: Dominic Hamon <dominichamon@users.noreply.github.com>