Cycles: Report build flags used for the OpenCL kernel compilation

For now it's reported to the stdout, matching to the CUDA behavior.
In the future we can hide this into GLog logging once the kernels
are considered all stable and so.

intern/cycles/device/device_opencl.cpp

@@ -676,6 +676,10 @@ public:
 
 		double starttime = time_dt();
 		printf("Compiling OpenCL kernel ...\n");
+		/* TODO(sergey): Report which kernel is being compiled
+		 * as well (megakernel or which of split kernels etc..).
+		 */
+		printf("Build flags: %s\n", custom_kernel_build_options.c_str());
 
 		if(!build_kernel(kernel_program, custom_kernel_build_options, debug_src))
 			return false;