raptor2: enable shared libraries by default

pkgs/development/libraries/librdf/raptor2.nix

@@ -1,4 +1,16 @@
-{ lib, stdenv, libxml2, libxslt, pkg-config, cmake, fetchFromGitHub, perl, bison, flex, fetchpatch }:
+{ lib
+, stdenv
+, libxml2
+, libxslt
+, pkg-config
+, cmake
+, fetchFromGitHub
+, perl
+, bison
+, flex
+, fetchpatch
+, static ? stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation rec {
   pname = "raptor2";
@@ -11,6 +23,11 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-h03IyFH1GHPqajfHBBTb19lCEu+VXzQLGC1wiEGVvgY=";
   };
 
+  cmakeFlags = [
+    # Build defaults to static libraries.
+    "-DBUILD_SHARED_LIBS=${if static then "OFF" else "ON"}"
+  ];
+
   patches = [
     # https://github.com/dajobe/raptor/pull/52
     (fetchpatch {