Small release to replace broken v1.6.2 release

What's Changed

• Stop generating the export header and just check it in by @dominichamon in https://github.com/google/benchmark/pull/1435
• use target_compile_definitions by @dominichamon in https://github.com/google/benchmark/pull/1440
• simplified code by @maochongxin in https://github.com/google/benchmark/pull/1439

New Contributors

• @maochongxin made their first contribution in https://github.com/google/benchmark/pull/1439

Full Changelog: https://github.com/google/benchmark/compare/v1.6.2...v1.7.0