Rename #define BENCHMARK or allow disabling benchmark feature

[mloskot]

Description

The #define BENCHMARK in a9b6813#diff-c06d59fb4f39c13fb9a355b49d321fcfR52 is an unfortunate name, with high potential of clashes.

For example, it clashes with (older) benchmarking framework, see DigitalInBlue/Celero@dc68534#diff-f1b66ca763828028068774e33319efb4R137 The generic BENCHMARK name issue also reported to Celero DigitalInBlue/Celero#114

It would be extremely helpful Catch offers a #define to allow disabling the whole benchmarking feature all the way.

[Ignition]

I may be missing something obvious, but is there a good reason why you have both Catch2 and Celero in the same translation unit?

[mloskot]

It happens, there are/were some files which included both (eg. shared fixtures for both, benchmark and test, so benchmark is actually tested for correctness - in non-optimised builds)