Fix T55054: possible use of unsupported instructions in Cycles texture code

Differential Revision: https://developer.blender.org/D5326

intern/cycles/kernel/kernels/cpu/kernel_cpu_image.h

@@ -19,6 +19,10 @@
 
 CCL_NAMESPACE_BEGIN
 
+/* Make template functions private so symbols don't conflict between kernels with different
+ * instruction sets. */
+namespace {
+
 template<typename T> struct TextureInterpolator {
 #define SET_CUBIC_SPLINE_WEIGHTS(u, t) \
   { \
@@ -523,6 +527,8 @@ ccl_device float4 kernel_tex_image_interp_3d(
   }
 }
 
+} /* Namespace. */
+
 CCL_NAMESPACE_END
 
 #endif  // __KERNEL_CPU_IMAGE_H__