Here are results from an i386 bulk build done with the base compiler updated to clang from LLVM 11.1.0 and the matching libc++. (ports/devel/llvm was not touched).
Some ports have failures that appear to be issues with the compiler/diff and I haven't listed them below; the following are problems with the ports themselves: inputmethods/scim-anthy: scim_anthy_prefs.cpp:223:9: error: type 'const char [1]' cannot be narrowed to 'bool' in initializer list [-Wc++11-narrowing] sysutils/sleuthkit: ./../fs/tsk_apfs.hpp:982:31: error: anonymous non-C-compatible type given name for linkage purposes by alias declaration; add a tag name here [-Werror,-Wnon-c-typedef-for-linkage] mail/kopano/core: mapi_wrap.cxx:35064:8: error: cannot initialize a variable of type 'bool' with an rvalue of type 'nullptr_t'