Sure. I basically did the following on trunk: $ CPP=/usr/bin/clang MAKEOBJDIRPREFIX=/private/var/tmp/obj ./tools/build/make.py TARGET=arm64 TARGET_ARCH=aar

Sure. I basically did the following on trunk: $ CPP=/usr/bin/clang MAKEOBJDIRPREFIX=/private/var/tmp/obj ./tools/build/make.py TARGET=arm64 TARGET_ARCH=aarch64 --host-compiler-type clang --debug -j17 --clean buildworld You probably can follow build(5) from FreeBSD hosts instead. NetBSD is similar, but you need to edit `tools/llvm/Makefile` and make sure that you use the following target for `support-modules` instead: support-modules: module-test.cpp Makefile - if ${HOST_CXX} -stdlib=libc++ -c -fmodules -fcxx-modules -fmodules-cache-path=./module.cache \ - ${.CURDIR}/module-test.cpp 3> /dev/null 2>&1; then \ - echo HOST_SUPPORTS_MODULES=yes > ${.TARGET}; \ - else \ - echo HOST_SUPPORTS_MODULES=no > ${.TARGET}; \ - fi + # Just don't use modules pre for C++20 targets. Some compilers cannot support them. + echo HOST_SUPPORTS_MODULES=no > ${.TARGET}; You can further speed up NetBSD builds by editing `share/mk/bsd.sys.mk` and removing the workaround for SunPro's cc. The repeated invocation of /bin/mv for each object file really does add up. I have not tried cross builds of OpenBSD from other operating systems.