Cleanup: fix various Cycles build warnings with non-default options

* Float/double promotion warnings were mainly meant for avoiding slow
  operatiosn in the kernel. Limit it to that to avoid hard to fix warnings
  in Hydra.
* Const warnings in Hydra iterators.
* Unused variable warnings when building without glog.
* Wrong camera enum comparisons in assert.
* PASS_UNUSED is not a pass type, only for pass offsets.

intern/cycles/kernel/CMakeLists.txt

@@ -733,6 +733,14 @@ if(CXX_HAS_AVX2)
   set_source_files_properties(device/cpu/kernel_avx2.cpp PROPERTIES COMPILE_FLAGS "${CYCLES_AVX2_KERNEL_FLAGS}")
 endif()
 
+# Warnings to avoid using doubles in the kernel.
+if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_C_COMPILER_ID MATCHES "Clang")
+  ADD_CHECK_CXX_COMPILER_FLAG(CMAKE_CXX_FLAGS _has_cxxflag_float_conversion "-Werror=float-conversion")
+  ADD_CHECK_CXX_COMPILER_FLAG(CMAKE_CXX_FLAGS _has_cxxflag_double_promotion "-Werror=double-promotion")
+  unset(_has_cxxflag_float_conversion)
+  unset(_has_cxxflag_double_promotion)
+endif()
+
 cycles_add_library(cycles_kernel "${LIB}"
   ${SRC_KERNEL_DEVICE_CPU}
   ${SRC_KERNEL_DEVICE_CUDA}