gnu: libxslt: Allow cross-compilation.

* gnu/packages/xml.scm (libxslt)[arguments]: Rewrite using gexps.
Add #:configure-flags.

gnu/packages/xml.scm

@@ -335,7 +335,8 @@ formulas and hyperlinks to multiple worksheets in an Excel 2007+ XLSX file.")
              (patches (search-patches "libxslt-generated-ids.patch"))))
     (build-system gnu-build-system)
     (arguments
-     `(#:phases (modify-phases %standard-phases
+     (list #:phases
+           #~(modify-phases %standard-phases
                (add-before 'check 'disable-fuzz-tests
                  (lambda _
                    ;; Disable libFuzzer tests, because they require
@@ -348,7 +349,18 @@ formulas and hyperlinks to multiple worksheets in an Excel 2007+ XLSX file.")
                    ;; circular dependency.
                    (substitute* "python/Makefile"
                      (("cd tests && \\$\\(MAKE\\) tests")
-                         "$(info Python tests are disabled by Guix.)")))))))
+                      "$(info Python tests are disabled by Guix.)")))))
+           #:configure-flags
+           (if (%current-target-system)
+               ;; 'configure.ac' uses 'AM_PATH_PYTHON', which looks for
+               ;; 'python' in $PATH, even though it's only used in the shebang
+               ;; of examples.  Thus, when cross-compiling, set 'PYTHON' so
+               ;; that 'configure' doesn't search $PATH.
+               #~(list (string-append "PYTHON="
+                                      #$(this-package-input
+                                         "python-minimal-wrapper")
+                                      "/bin/python"))
+               #~'())))
     (home-page "http://xmlsoft.org/XSLT/index.html")
     (synopsis "C library for applying XSLT stylesheets to XML documents")
     (inputs