gnu: findutils: Update XFAIL_TESTS for the hurd.

This could do with more investigating, but this reflects what I see locally.

* gnu/packages/base.scm (findutils)[arguments]: Update XFAIL_TESTS for the
hurd.
* gnu/packages/commencement.scm (findutils-boot0): Stop clearing the
make-flags, so the above change applies to findutils-boot0.

gnu/packages/base.scm

@@ -348,7 +348,7 @@ interactive means to merge two files.")
                        (("#!/bin/sh")
                         (string-append "#!" (which "sh")))))))
       #:make-flags ,(if (hurd-target?)
-                        ''("XFAIL_TESTS=test-perror2")
+                        ''("XFAIL_TESTS=test-strerror_r")
                         ''())))
    (synopsis "Operating on files matching given criteria")
    (description

gnu/packages/commencement.scm

@@ -2082,9 +2082,7 @@ exec " gcc "/bin/" program
                            (substitute* "gnulib-tests/Makefile"
                              (("^XFAIL_TESTS =")
                               "XFAIL_TESTS = test-fnmatch ")))))
-                     '())))
-           ((#:make-flags flags ''())
-            ''()))))))
+                     '()))))))))
 
 (define file
   (package