Applies to >=11.4-RELEASE (since the change to default i686): I'm using -march=pentium-mmx in a VM to build for my old dual Pentium MMX 233; so far so unremarkable. The first problem is that everything in /usr/obj/tmp/legacy/ is built with default flags, not CFLAGS, so it's built for i686 (CMOV*). Obviously that doesn't work when trying to installworld over nfs. Looking at #250755 I changed the default to i586, did a full build and install twice, and the resulting build runs OK. However, it's far from perfect - /usr/local/sbin/pkg-static somehow still gets compiled with CMOV, building ports fails somewhere I've yet to track down - yes, the system boots and runs, but it's not actually usable. Could CFLAGS, or at least -march=, be passed to *everything* please? AFAICT it's impossible to compile for <i686 as things stand without treating it as a full cross-compile; FreeBSD has always been able to build itself on the system it's running on, but right now a running i586 system *cannot* do that.
^Triage: clear unneeded flags. Nothing has yet been committed to be merged.