Cycles: Don't silence unused macro, remove the macro instead

It's not really handy to silence something unused hoping for it'll be
used in the future. We can end up with quite some silencing then.

Also made this flag which i find rather useless to NOT cause -Werror
in Cycles code.

intern/cycles/CMakeLists.txt

@@ -202,8 +202,10 @@ endif()
 if(CMAKE_COMPILER_IS_GNUCXX)
 	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")
+	ADD_CHECK_CXX_COMPILER_FLAG(CMAKE_CXX_FLAGS _has_no_error_unused_macros "-Wno-error=unused-macros")
 	unset(_has_cxxflag_float_conversion)
 	unset(_has_cxxflag_double_promotion)
+	unset(_has_no_error_unused_macros)
 endif()
 
 

intern/cycles/util/util_path.cpp

@@ -34,14 +34,9 @@ OIIO_NAMESPACE_USING
 #  include <direct.h>
 #else
 #  define DIR_SEP '/'
-#  define DIR_SEP_ALT '\\'
 #  include <dirent.h>
 #endif
 
-#if defined(DIR_SEP_ALT)
-/* quiet unused define warning */
-#endif
-
 #ifdef HAVE_SHLWAPI_H
 #  include <shlwapi.h>
 #endif