+ libdrm depends_on libpciaccess. Use spack provided libpciaccess.

var/spack/repos/builtin/packages/libdrm/package.py

@@ -2,7 +2,7 @@
 
 class Libdrm(Package):
     """A userspace  library for  accessing the  DRM, direct
-    rendering  manager, on  Linux,  BSD and  other  operating 
+    rendering  manager, on  Linux,  BSD and  other  operating
     systems that support the  ioctl interface."""
 
     homepage = "http://dri.freedesktop.org/libdrm/" # no real website...
@@ -11,6 +11,8 @@ class Libdrm(Package):
     version('2.4.59', '105ac7af1afcd742d402ca7b4eb168b6')
     version('2.4.33', '86e4e3debe7087d5404461e0032231c8')
 
+    depends_on('libpciaccess')
+
     def install(self, spec, prefix):
         configure("--prefix=%s" % prefix)