[sreeram-11]

Windows ROCm builds randomly took 2-4h even when the source hadn't changed.

Problem

• Whenever the cached ROCm install got evicted, ROCm was reinstalled.
• pip gives clang.exe a new modified time on every install, and with ccache's default compiler_check=mtime that makes every cache lookup miss.
• Ubuntu got this fix in August (11cded4) but Windows never did.

Fix

1. Set ccache to compiler_check=content (+ Ubuntu's sloppiness flags) in windows-rocm, matching ubuntu-24-rocm.
2. Removed the rocm-wheels cache and now install ROCm every run, like Ubuntu. Costs ~1 min per job but frees ~3.3 GB of the repo's 10 GB cache quota, which we're currently over.
3. Bumped ggml-org/ccache-action from v1.2.16 to v1.2.21 (ccache 4.9 to 4.13), so each run's Summary page shows ccache hit/miss stats. The build logs are ~1.5 GB and get truncated, so the stats never show up there.

Notes

• The first run on this PR will be a full cold build (~3.5-4h per Windows ROCm job), because the ccache hash method and version both changed. When re-run after the first run finishes, the Windows ROCm builds should then take ~10 min, with near-100% hits under "CCache Statistics".
• This doesn't fix runs where upstream touches core headers (ggml.h, common.cuh, etc.). Those force a full rebuild on both Windows and Ubuntu and will still take 2.5-4h.
• The old rocm-wheels-*-Windows-v2 caches are no longer used and will age out on their own (or can be deleted manually).

[superm1]

Please send same upstream

[sreeram-11]

@superm1,

Bumping ccache-action from v1.2.16 to v1.2.21 in this PR is what actually fixed the Windows ROCm build jobs. Starting from v1.2.21, the action sets compiler_check=content on Windows by itself. The explicit "Tune ccache" step added here is redundant but harmless.

This change isn't needed upstream. Upstream already uses ggml-org/ccache-action@v1.2.24 (which sets compiler_check=content on Windows) and doesn't have a ROCm wheel cache. Its Windows ROCm builds take 3 to 6 min every run, with ccache stats of 154 hits out of 155.

[superm1]

IMO I would just mirror what upstream does. Redundancy is tech debt.