tweak scripts/build_android.sh for ABI and header install (#20152)
Summary:
We now can build libtorch for Android.
This patch aims to provide two improvements to the build
- Make the architecture overridable by providing an environment variable `ANDROID_ABI`.
- Use `--target install` when calling cmake to actually get the header files nicely in one place.
I ran the script without options to see if the caffe2 builds are affected (in particularly by the install), but they seem to run OK and probably only produce a few files in build_android/install.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20152
Differential Revision: D15249020
Pulled By: pjh5
fbshipit-source-id: bc89f1dcadce36f63dc93f9249cba90a7fc9e93d
