audacity: minor update, prefer system-wide libs

- Using system-wide libs where we have them (except for portaudio, which
  I couldn't make work).
- Add the soxr library (now the preferred way of audio resampling).

pkgs/applications/misc/audio/soxr/default.nix

@@ -0,0 +1,20 @@
+{ stdenv, fetchurl, cmake }:
+
+stdenv.mkDerivation rec {
+  name = "soxr-0.1.1";
+
+  src = fetchurl {
+    url = "mirror://sourceforge/soxr/${name}-Source.tar.xz";
+    sha256 = "1hmadwqfpg15vhwq9pa1sl5xslibrjpk6hpq2s9hfmx1s5l6ihfw";
+  };
+
+  preConfigure = ''export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:"`pwd`/build/src'';
+
+  buildInputs = [ cmake ];
+
+  meta = {
+    description = "An audio resampling library";
+    homepage = http://soxr.sourceforge.net;
+    license = "LGPLv2.1+";
+  };
+}