GNUmakefile: Don't install part of hashsum if we excluded hashsum

[oech3]

Don't try to install part of hashsum if we excluded hashsum.

Test on main is blocked by wrong install operation. This should fix it.
related #9009

[codspeed-hq]

CodSpeed Performance Report

Merging #9036 will improve performances by 3.04%

_{Comparing oech3:clear-hashsum (026ef1b) with main (28bc57a)}

Summary

⚡ 2 improvements
✅ 103 untouched
⏩ 74 skipped¹

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	du_human_balanced_tree[(5, 4, 10)]	10.4 ms	10.1 ms	+3.04%
⚡	du_summarize_balanced_tree[(5, 4, 10)]	8.5 ms	8.3 ms	+2.54%

Footnotes

1. 74 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[oech3]

Ready to merge. hashsum multicall is complex at least for me...

[cakebaker]

Thanks!

Ready to merge. hashsum multicall is complex at least for me...

Yeah, hopefully we can get rid of it in the future.

[oech3]

Would you fix #9009 too? I'll drop extra option if needed. (Failing is CodSpeed)