ABCL 1.9.1 regression: COMPILE-FILE-PATHNAME

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.