Cycles: Add an AVX kernel for CPU rendering.

* AVX is available on Intel Sandy Bridge and newer and AMD Bulldozer and newer.
* We don't use dedicated AVX intrinsics yet, but gcc auto vectorization gives a 3% performance improvement for Caminandes. Tested on an i5-3570, Linux x64.
* No change for Windows yet, MSVC 2008 does not support AVX.

Reviewed by: brecht
Differential Revision: https://developer.blender.org/D216

intern/cycles/util/util_system.cpp

@@ -198,6 +198,12 @@ bool system_cpu_support_sse41()
 	CPUCapabilities& caps = system_cpu_capabilities();
 	return caps.sse && caps.sse2 && caps.sse3 && caps.ssse3 && caps.sse41;
 }
+
+bool system_cpu_support_avx()
+{
+	CPUCapabilities& caps = system_cpu_capabilities();
+	return caps.sse && caps.sse2 && caps.sse3 && caps.ssse3 && caps.sse41 && caps.avx;
+}
 #else
 
 bool system_cpu_support_sse2()
@@ -210,6 +216,16 @@ bool system_cpu_support_sse3()
 	return false;
 }
 
+bool system_cpu_support_sse41()
+{
+	return false;
+}
+
+bool system_cpu_support_avx()
+{
+	return false;
+}
+
 #endif
 
 CCL_NAMESPACE_END