volume: Add Orc-based optimised volume scaling

This adds volume scaling for 1- and 2-channel software volume scaling
using Orc. While testing the MMX and SSE backends on a Core2, I see an
~2x performance benefit over the hand-rolled MMX and SSE code. Since I
haven't been able to test on other architectures, the Orc code is only
used when MMX/SSE* is present. This can be changed in the future after
testing on AMD and ARM machines.

src/pulsecore/cpu-orc.h

@@ -0,0 +1,37 @@
+#ifndef foocpuorchfoo
+#define foocpuorchfoo
+
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2010 Arun Raghavan <arun.raghavan@collabora.co.uk>
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2.1 of the License,
+  or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pulsecore/cpu.h>
+
+/* Orc-optimised bits */
+
+void pa_cpu_init_orc(pa_cpu_info cpu_info);
+
+void pa_volume_func_init_orc(void);
+
+#endif /* foocpuorchfoo */