[Build] Reflect Compile-Time CMake Options into libtvm.so

[junrushao]

Reflecting build time info (git commit hash, cmake flags and options, etc) is very helpful in TVM development, packaging, and especially trouble shooting. This PR showcases how to incorporate compile-time information into TVM library, specifically, git commit hash in this PR. Other flags can be done in similar fashion, by just appending lines like "TVM_USE_CUDA=${USE_CUDA}" in the CMakeList.txt.

How to use this functionality. Run the command below:

> python -c "import tvm; print(tvm.support.libinfo())"
{"GIT_COMMIT_HASH": "921d4e0efea280c149940669bb23ef8c4de366e9"}

Per discussion with @jroesch. CC: @jwfromm @tqchen.

[tqchen]

Thanks @junrushao1994 we will need also to support the build where the code base is not part of a git repo(e.g. in a tarball during release).

[junrushao]

@tqchen If so, we don't have a git commit id, is that correct?

[tqchen]

Yes, we can skip the info if that is the case

[junrushao]

I see. We should set it to something like “git-not-found” then

[junrushao]

@tqchen I updated the script accordingly. Now if it is not in a git repo, or git executable is not found, the result will be:

> python -c "import tvm; print(tvm.support.libinfo())"
{"GIT_COMMIT_HASH": "NOT-FOUND"}

[junrushao]

CI is green now. Could you take another look @tqchen?

[tqchen]

Thanks @junrushao1994 @jroesch !