DEFSYSTEM: multiple :DEPENDS-ON are not merged
CL-USER> (asdf:asdf-version)
"3.3.4"
CL-USER> (asdf:defsystem #:foo
:depends-on (#:bar)
:depends-on (#:baz)
:depends-on (#:quux))
#<ASDF/SYSTEM:SYSTEM "foo">
CL-USER> (asdf:system-depends-on (asdf:find-system :foo))
("bar")