/usr/lib/ecl-15.3.7/rt.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 "rt" :class asdf::prebuilt-system
:lib #P"SYS:LIBRT.A"
:depends-on NIL
:components ((:compiled-file "rt" :pathname #P"SYS:RT.FAS")))
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