/usr/lib/ecl-15.3.7/prebuilt-asdf.asd is in ecl 15.3.7+dfsg1-2+deb9u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | (defsystem "prebuilt-asdf" :class asdf::prebuilt-system
:lib #P"SYS:LIBASDF.A"
:depends-on ("cmp")
:components ((:compiled-file "prebuilt-asdf" :pathname #P"SYS:ASDF.FAS")))
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