gnu: dante: Enable preloading support.

Fixes <https://issues.guix.gnu.org/63250>.

Dante uses dlopen which doesn't work with libc.so but libc.so.6.
This fixes socksify, which is patched to skip invoking uname needlessly.

* gnu/packages/networking.scm (dante): Enable preloading support.
* gnu/packages/patches/dante-non-darwin.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.

References: https://github.com/NixOS/nixpkgs/pull/68418#discussion_r343625853
Change-Id: I03a5b6b6e11cf6a0453a4968ff00c6dd627249a8
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/local.mk

@@ -1066,6 +1066,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/cursynth-wave-rand.patch			\
   %D%/packages/patches/cvs-CVE-2017-12836.patch		\
   %D%/packages/patches/d-feet-drop-unused-meson-argument.patch	\
+  %D%/packages/patches/dante-non-darwin.patch			\
   %D%/packages/patches/date-output-pkg-config-files.patch	\
   %D%/packages/patches/datefudge-gettimeofday.patch		\
   %D%/packages/patches/dbacl-include-locale.h.patch		\

gnu/packages/networking.scm

@@ -3640,13 +3640,10 @@ and check if the WLAN key or the master key was transmitted unencrypted.")
        (uri (string-append "https://www.inet.no/dante/files/dante-"
                            version ".tar.gz"))
        (sha256
-        (base32 "0pbahkj43rx7rmv2x40mf5p3g3x9d6i2sz7pzglarf54w5ghd2j1"))))
+         (base32 "0pbahkj43rx7rmv2x40mf5p3g3x9d6i2sz7pzglarf54w5ghd2j1"))
+       (patches (search-patches "dante-non-darwin.patch"))))
     (build-system gnu-build-system)
-    (arguments
-     ;; XXX: The dynamic socks library doesn't work with 'libc.so' (GNU ld
-     ;; script).  When preloading is enabled, 'sockd' failed with:
-     ;;    … Failed to open library "libc.so": …: invalid ELF header
-     '(#:configure-flags '("--disable-preload")))
+    (arguments '(#:configure-flags '("--with-libc=libc.so.6")))
     (home-page "https://www.inet.no/dante/")
     (synopsis "SOCKS server and client")
     (description "Dante is a SOCKS client and server implementation.  It can

gnu/packages/patches/dante-non-darwin.patch

@@ -0,0 +1,15 @@
+Disable runtime check for Darwin so we don't have to substitute uname.
+--- a/bin/socksify.in
++++ b/bin/socksify.in
+@@ -65,11 +65,6 @@
+     unset FULLPATH
+ fi
+ 
+-#use "FLAT_NAMESPACE" on Darwin in attempt to match LD_PRELOAD behavior
+-if test x`uname` = xDarwin; then
+-    export DYLD_FORCE_FLAT_NAMESPACE=t
+-fi
+-
+ #dlib/Makefile.am libtool flags should produce a predictable library name
+ #(ending in SOLIB_POSTFIX).
+ LIBRARY="${SOCKS_LIBRARY:-${FULLPATH}libdsocks.@SOLIB_POSTFIX@}"