xercesc: Use curl network backend

The default `socket` backend does not support TLS.
As a result, attempting to validate the following GPX file with
`SAX2Count -v=always foo.gpx` would fail with `unsupported protocol in URL`
because the Garmin URLs redirect to HTTPS.

    <gpx version="1.1" creator="foo" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 https://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd" xmlns="http://www.topografix.com/GPX/1/1" xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"></gpx>

Let’s switch to curl backend.

pkgs/development/libraries/xercesc/default.nix

@@ -1,4 +1,8 @@
-{ lib, stdenv, fetchurl }:
+{ stdenv
+, lib
+, fetchurl
+, curl
+}:
 
 stdenv.mkDerivation rec {
   pname = "xerces-c";
@@ -9,8 +13,16 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-PY7Bx/lOOP7g5Mpa0eHZ2yPL86ELumJva0r6Le2v5as=";
   };
 
-  # Disable SSE2 extensions on platforms for which they are not enabled by default
-  configureFlags = [ "--disable-sse2" ];
+  buildInputs = [
+    curl
+  ];
+
+  configureFlags = [
+    # Disable SSE2 extensions on platforms for which they are not enabled by default
+    "--disable-sse2"
+    "--enable-netaccessor-curl"
+  ];
+
   enableParallelBuilding = true;
 
   meta = {