GNUmakefile: prefer system {ln,install}.exe #13390

Job	Run time
Style/lint (windows-latest, feat_os_windows)	2m 22s
Style/format (ubuntu-latest, feat_os_unix)	10s
Style/lint (macos-latest, feat_os_macos)	1m 36s
Style/spelling (ubuntu-latest, feat_os_unix)	1m 5s
Style/toml	12s
Style/lint (ubuntu-latest, all, true)	1m 23s
Pre-commit hooks	21s
Style/Python	8s
	7m 17s

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