[BUG] Passing -pedantic -Werror but relying on extensions

[AaronBallman]

The build script passes -pedantic -Werror:

benchmark/CMakeLists.txt

Line 207 in 4e26a9e

add_cxx_compiler_flag(-pedantic)

However, the code relies on extensions:

benchmark/include/benchmark/benchmark.h

Line 1484 in 4e26a9e

#if defined(__COUNTER__) && (__COUNTER__ + 1 == __COUNTER__ + 0)

While working on implementing __COUNTER__ for C2y mode in Clang (llvm/llvm-project#162662), I've added the expected extension and pre-compat warnings, which then cause the code in benchmark.h to fail to compile because of -pedantic-errors.

There's a few ways to solve this, but I'm not familiar enough with benchmark to know which is the best way to go. You could stop using __COUNTER__ entirely and just use the __LINE__ fallback since that has to work to be a useful fallback anyway. You could stop passing -pedantic and continuing using __COUNTER__. You could use __extension__ to silence the extension warning. Other ideas likely exist.

[LebedevRI]

I think this particular warning would just need to be silenced in this paricular case.
Loosening requested warning flags runs the risk of allowing other extensions slipping in
(well, not really, but better to just not go there i'd say.)