support pre-generate bindings for aarch64

[glorv]

follow #356 this pr support pre generated binding for aarch64, so we can get rid of depending on newer version of clang.

Signed-off-by: glorv glorvs@163.com

[BusyJay]

Thanks for your contribution. But I'm worry about the maintenance of the feature. On one hand, the bindings should be tested by CI to ensure the generated bindings actually work. On the other hand, because we don't have machines that are aarch64 based. It will be broken when we are trying to upgrade grpc c core.

[glorv]

Thanks for your contribution. But I'm worry about the maintenance of the feature. On one hand, the bindings should be tested by CI to ensure the generated bindings actually work. On the other hand, because we don't have machines that are aarch64 based. It will be broken when we are trying to upgrade grpc c core.

• we can add test for arm64 either in travis-ci or in our ci, and if necessary, we can add extra test cases to make sure all the bindings are properly generated.
• we already had aarch64 machine now, and we have done many tests on aarch64 machine provided by Huawei, so it is not hard to dev or run test on aarch64 arch machine if needed. From v4.0, we will start release aarch64 tidb package, so we will also run consistent test on aarch machines.

[glorv]

@BusyJay PTAL

[hunterlxt]

generating bindgen needs LLVM support

[glorv]

yes. It seems the default CI environment already install llvm tool chains. On the other hand, there are no llvm apt repo available on aarch64/linux, thus made it hard to install llvm tool chain on this platform, so just use the system default packages maybe a good idea currently.

[glorv]

@hunterlxt PTAL again~

[hunterlxt]

Thanks for your contribution.