repair executable-relative boot file search on NetBSD #393

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	29m 8s
ci (a6osx, macos-13)	16m 28s
ci (ta6osx, macos-13)	20m 6s
ci (arm64osx, macos-14)	8m 58s
ci (tarm64osx, macos-14)	10m 30s
ci (i3le, ubuntu-22.04)	12m 35s
ci (ti3le, ubuntu-22.04)	15m 57s
ci (a6le, ubuntu-22.04)	8m 55s
ci (ta6le, ubuntu-22.04, CFLAGS+=-std=gnu89)	12m 2s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 6s
ci (i3nt, windows-2022, vs)	11m 32s
ci (ti3nt, windows-2022, vs)	14m 41s
ci (a6nt, windows-2022, vs)	11m 47s
ci (ta6nt, windows-2022, vs)	14m 27s
ci (ta6nt, windows-2022, gcc, CFLAGS+=-std=gnu89)	13m 1s
ci (ta6le, ubuntu-22.04, test-more, more)	57m 35s
	4h 25m 48s

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