[bug#41830] xl2tpd fixes

[Ivan Kozlov]

xl2tpd runs pppd to complete the connection. It also includes some of the Linux 
headers (and uses fallbacks otherwise).

--- 
/gnu/store/869i2xd7jih9cdcrccwk8rsxycwksjba-guix-module-union/share/guile/site/3.0/gnu/packages/vpn.scm
+++ #<buffer vpn.scm>
@@ -576,9 +576,18 @@
      `(#:make-flags (list (string-append "PREFIX=" %output)
                           "CC=gcc")
        #:phases (modify-phases %standard-phases
+                  (add-before 'build 'setup-environment
+                    (lambda* (#:key inputs #:allow-other-keys)
+                      (setenv "CFLAGS" (string-append "-DPPD=\""
+                                                      (assoc-ref inputs "ppp")
+                                                      "/sbin/pppd\""))
+                      (setenv "KERNELSRC" (assoc-ref inputs 
"linux-libre-headers"))
+                      #t))
                   (delete 'configure))  ; no configure script
        #:tests? #f))                    ; no tests provided
-    (inputs `(("libpcap" ,libpcap)))
+    (inputs `(("libpcap" ,libpcap)
+              ("linux-libre-headers" ,linux-libre-headers)
+              ("ppp" ,ppp)))
     (home-page "https://www.xelerance.com/software/xl2tpd/";)
     (synopsis "Layer 2 Tunnelling Protocol Daemon (RFC 2661)")
     (description

Diff finished.  Fri Jun 12 20:38:14 2020