repair executable-relative boot file search on NetBSD #394

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	29m 49s
ci (a6osx, macos-13)	14m 33s
ci (ta6osx, macos-13)	18m 4s
ci (arm64osx, macos-14)	8m 15s
ci (tarm64osx, macos-14)	10m 50s
ci (i3le, ubuntu-22.04)	12m 42s
ci (ti3le, ubuntu-22.04)	15m 45s
ci (a6le, ubuntu-22.04)	8m 49s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	12m 6s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 21s
ci (i3nt, windows-2022, vs)	11m 45s
ci (ti3nt, windows-2022, vs)	16m 12s
ci (a6nt, windows-2022, vs)	11m 38s
ci (ta6nt, windows-2022, vs)	15m 14s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 6s
ci (ta6le, ubuntu-22.04, test-more, more)	57m 5s
	4h 24m 14s

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