pgpgme: Fix build with python on macOS

* Replace LD_LIBRARY_PATH with OS-specific name (e.g. DYLD_LIBRARY_PATH
  on macOS).
* Disable Python tests on macOS, because they use gpg, which fails due
  to a very long socket path (https://github.com/NixOS/nix/pull/1085).

The former should be fixed upstream. The latter is a Nix-specific issue,
but it can be worked-around upstream by making Python tests respect
--disable-gpg-test.

pkgs/development/libraries/gpgme/default.nix

@@ -49,6 +49,15 @@ stdenv.mkDerivation rec {
 
   postPatch =''
     substituteInPlace ./configure --replace /usr/bin/file ${file}/bin/file
+  ''
+  # Apply only on Darwin to save rebuilds on Linux
+     + lib.optionalString stdenv.isDarwin ''
+    sed -i "s/LD_LIBRARY_PATH/@shlibpath_var@/" lang/python/tests/Makefile.in
+    sed -i "s/ac_subst_vars='/ac_subst_vars='shlibpath_var\n/" configure
+  ''
+  # Disable python tests on Darwin as they use gpg (see configureFlags below)
+     + lib.optionalString stdenv.isDarwin ''
+    sed -i "s/SUBDIRS = \. tests/SUBDIRS = ./" lang/python/Makefile.in
   '';
 
   configureFlags = [