When make installworld is run after building with WITHOUT_LIB32 set in /etc/src.conf the dirs /usr/lib32 /usr/lib32/dtrace and /usr/lib32/i18n still get created with no files inside. The issue with that is that some ports use the existence of /usr/lib32 to decide whether to build 32bit versions. devel/valgrind is an example. Deleting the dirs solves the port build issues. How-To-Repeat: Set WITHOUT_LIB32 in /etc/src.conf and then make buildworld then make installworld
This has been fixed in 11-Release.