What is the meaning of 10000 in the triple aarch64-linux-android10000?
Is it perhaps Android version (10.000)?
There is a similar question posted on Android Help Community (support.google.com/android). The answer is to "find the information you need on the Android Developers' forum". I found this question on Android Developers' forum (forums.androidcentral.com). The answer is to "ask this question at XDA Forum". I couldn't find this question on XDA Forum (xdaforums.com), because couldn't find the "search" / "find" option / feature there.
UPD. Links to the source where aarch64-linux-android10000 is used: https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/+/refs/tags/ndk-r23-beta2/BUILD.bazel#118.
By examining LLVM's source code I found that number 10000 is used to set "maximum API level". It seems that the 10000 was chosen "with a big margin" and currently can be, for example, 777.