I just looked at the Maxima build problem, which I wasn't aware of until I saw the recent message that mentioned it. ABCL 1.9.0's COMPILE-FILE-PATHNAME did not cause the problem; it behaved correctly according to the CL spec.
Here is the value of
(compile-file-pathname "/mnt/maxima-5.46.0/src/numerical/f2cl-package.lisp" :output-file "binary-abcl/numerical/f2cl-package.abcl")
in four Lisps (CCL 1.12.1, SBCL 2.1.1.debian, ABCL 1.9.0, and ABCL 1.9.1):
#P"/mnt/maxima-5.46.0/src/numerical/binary-abcl/numerical/f2cl-package.abcl" #P"/mnt/maxima-5.46.0/src/numerical/binary-abcl/numerical/f2cl-package.abcl" #P"/mnt/maxima-5.46.0/src/numerical/binary-abcl/numerical/f2cl-package.abcl" #P"/mnt/maxima-5.46.0/src/binary-abcl/numerical/f2cl-package.abcl"
As you can see, the last one (ABCL 1.9.1) is the one that diverges.
I repeated that test for all of the COMPILE-FILE-PATHNAME invocations in the failed Maxima build. In every case, CCL and SBCL and ABCL 1.9.0 confirmed each others' results.
ABCL 1.9.0's COMPILE-FILE-PATHNAME produced bad output only because it received bad input.