Qt4 builds successfully with proper RPATHs.

var/spack/packages/xz/package.py

@@ -0,0 +1,16 @@
+from spack import *
+
+class Xz(Package):
+    """XZ Utils is free general-purpose data compression software with
+       high compression ratio. XZ Utils were written for POSIX-like
+       systems, but also work on some not-so-POSIX systems. XZ Utils are
+       the successor to LZMA Utils."""
+    homepage = "http://tukaani.org/xz/"
+    url      = "http://tukaani.org/xz/xz-5.2.0.tar.bz2"
+
+    version('5.2.0', '867cc8611760240ebf3440bd6e170bb9')
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")