Add GitHub workflow for building+installing into toolchain via CMake.

[dan-zheng]

Add GitHub Actions workflow for:

• Downloading and installing a swift.org/download macOS development snapshot
• Building tensorflow/swift-apis via CMake
• Installing tensorflow/swift-apis into the toolchain via CMake
• Repackaging the toolchain into a .pkg
• Publishing the toolchain .pkg artifact

This allows users to download standard swift.org/download toolchains with
TensorFlow and X10 installed.

[compnerd]

I think that if we are doing this, it would be nice to do all the targets (or at least the ones that are on GHA).

[compnerd]

I think that this needs to be made conditional. This will do a GH release per PR.

[dan-zheng]

That's a good point. I wonder what do you think is a good condition, and how to add it?

[dan-zheng]

I tried adding some conditional steps, but they still seem to run unconditionally even when the guard condition is false. Any clue why or how to do better?

swift-apis/.github/workflows/macOS-CMake-toolchain.yml

Lines 83 to 99 in 0ba6914

	- name: Build toolchain package installer
	if: env.should_build_toolchain_installer
	run: |
	TOOLCHAIN_ROOT_LOCATION="/Library/Developer/Toolchains/${TOOLCHAIN_NAME}.xctoolchain"
	TF_TOOLCHAIN_NAME="swift-tensorflow-DEVELOPMENT-SNAPSHOT-${TOOLCHAIN_DATE}-a"
	pkgbuild --identifier org.tensorflow-${TOOLCHAIN_SHORT_DATE} \
	--install-location ${TOOLCHAIN_ROOT_LOCATION} \
	--version 5.0.${TOOLCHAIN_SHORT_DATE} \
	--root ${DEST_TOOLCHAIN_LOCATION} \
	${TF_TOOLCHAIN_NAME}-osx.pkg
	- name: Upload toolchain package installer
	if: env.should_build_toolchain_installer
	uses: actions/upload-artifact@v2
	with:
	name: swift-tensorflow-DEVELOPMENT-SNAPSHOT-${{ env.toolchain_date }}-a-osx.pkg
	path: '*.pkg'

https://github.com/tensorflow/swift-apis/runs/1660455199

[compnerd]

I suppose that we could do this on tags only. I think that tags are uncommon enough where it may make sense for building on a tag even when its not an actual release but some point that we want to archive.

[dan-zheng]

The repackaged toolchains built as part of this GitHub action are currently not right (way too small, much is missing). I'm not sure why, would be good to investigate. This action is still useful for testing CMake-based builds and installs.