support build efsw in bazel toolchain

[ashione]

Create a bazel workspace meta data and make users can acccess in bazel repo.
More details can get from website Bazel intro https://bazel.build/about/intro.

My laptop version passes all of building, and env :

• OS : both centos7 and macos 11.5.1
• bazel version : 4.2.1
• gcc 9.2.1

[ashione]

BTW, anyone can build it in windows might help us to verify the last OS since I can not access any windows PC right here.

[SpartanJ]

Thank you very much for your contribution! I left some minor comments. But, I'm not sure if adding this to the main repository makes sense. I cannot maintain every single build system people need to use with efsw, and bazel is a very specific and complex build system, primarily used in AI environments. I'll think about it. I also don't have the Windows environment ready to test with bazel.

[ashione]

Thank you very much for your contribution! I left some minor comments. But, I'm not sure if adding this to the main repository makes sense. I cannot maintain every single build system people need to use with efsw, and bazel is a very specific and complex build system, primarily used in AI environments. I'll think about it. I also don't have the Windows environment ready to test with bazel.

Never mind. I just find this repo can me watch file or directory changes that's really helpful. Bazel is easy to use and it's pleasure to maintain this toolchain in this repo if you make the decision to merge this into mainstream.

More and more repo support mutilple build tools. Absl is a basic library, for example, https://github.com/abseil/abseil-cpp, has both cmake and bazel building ways.