gnu: groff: Disable relocatability.

* gnu/packages/groff.scm (groff)[arguments]<#:phases>[disable-relocatability]:
New phase.

gnu/packages/groff.scm

@@ -62,6 +62,34 @@
     `(#:parallel-build? #f   ; parallel build fails
       #:phases
       (modify-phases %standard-phases
+        (add-after 'unpack 'disable-relocatability
+          (lambda _
+            ;; Groff contains a Rube Goldberg-esque relocator for the file
+            ;; "charset.alias".  It tries to find the current executable
+            ;; using realpath, a do-it-yourself search in $PATH and so on.
+            ;; Furthermore, the routine that does the search is buggy
+            ;; in that it doesn't handle error cases when they arise.
+            ;; This causes preconv to segfault when trying to look up
+            ;; the file "charset.alias" in the NULL location.
+            ;; The "charset.alias" parser is a copy of gnulib's, and a
+            ;; non-broken version of gnulib's "charset.alias" parser is
+            ;; part of glibc's libcharset.
+            ;; However, groff unconditionally uses their own
+            ;; "charset.alias" parser, but then DOES NOT INSTALL the
+            ;; file "charset.alias" when glibc is too new.
+            ;; In Guix, our file "charset.alias" only contains an obscure
+            ;; alias for ASCII and nothing else.  So just disable relocation
+            ;; and make the entire "charset.alias" lookup fail.
+            ;; See <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=30785> for
+            ;; details.
+            (substitute* "src/libs/libgroff/Makefile.sub"
+             (("-DENABLE_RELOCATABLE=1") ""))
+            ;; That file contains a crash bug--so make sure that
+            ;; its contents are not there.
+            (call-with-output-file "src/libs/libgroff/relocate.cpp"
+              (lambda (port)
+                #t))
+            #t))
         (add-after 'unpack 'setenv
           (lambda _
             (setenv "GS_GENERATE_UUIDS" "0")