[script] leverage slc SDK cache and add ccache to speedup incremental builds

[lmnotran]

Summary of changes

• slc
  • Remove the --clear-cache flag to leverage SDK cache
  • Switch to using daemon-mode. Reduces slc startup time
• Add ccache to build scripts for potential build speedups. See more below
• GitHub Actions
  • Only pull required LFS files
  • Cache ARM Toolchain between builds

---

CCache

When building with no compiler cache, the build proceeds as normal and takes a normal amount of time. For the Build/arm-gcc-* workflows, it usually takes ~20-30 min for the workflow to run completely.

Example: Build/arm-gcc-12.2.Rel1 (no compiler cache)

If you examine this run, you can see during the setup, there's no cache found (log here). Looking at the ccache statistics during teardown, you can see there was a very low cache hit rate.

ccache hits: 2.05 %
Time spent in Build step: 22m 22s

Example: Build/arm-gcc-12.2.Rel1 (with compiler cache)

During this second run, a compiler cache was located and added to the workspace. This speedup is also reflected in the ccache statistics.

ccache hits: 99.46 %
Time spent in Build step: 2m 52s

These performance gains are not limited to GitHub actions builds. CCache has been added to the script/build and script/build-example-apps scripts, meaning builds on development machines will also benefit from the same speedup potential.

One thing to note is that ccache will bring the most benefit when iterating on changes. Of course, the speedup will be reduced in scenarios where the cache cannot be leveraged, including but not limited to the first build when building for a board you haven't built before, switching branches, or making any wide-reaching changes.

[suveshpratapa]

@lmnotran There should be no user facing changes from this, I assume? One would continue to use slc as before and just notice improvements when iterating on a build? Are there any pitfalls to watch out for / build dirs to clear if we do want a fresh build?

[lmnotran]

@suveshpratapa

@lmnotran There should be no user facing changes from this, I assume? One would continue to use slc as before and just notice improvements when iterating on a build?

Nope! There are no user-facing changes. Users will continue to build in the same way as they have been before. They don't even need to install/use ccache if they don't want to. It's only used when ccache is present in the user's PATH.

Are there any pitfalls to watch out for / build dirs to clear if we do want a fresh build?

Nope! ccache is aware of the changes that would determine if the compiler cache is able to be leveraged safely or not. If a user is looking to do a fresh/clean build, they can just delete the build/ folder and a fresh build will happen, leveraging the compiler cache when possible. See more on how ccache works: https://ccache.dev/manual/4.8.2.html#_how_ccache_works

[suveshpratapa]

LGTM

[romacdon]

LGTM - do we want to squash commits?

[lmnotran]

LGTM - do we want to squash commits?

Squash on merge is fine. I'd like to keep them separate in the branch though. They're all independent and separate changes/ideas

[lmnotran]

@jwhui could you review this when you get a chance please? Thanks!