As found by Peter Kay on misc, qt5 detects CPU features to enable at build time, so produces binaries that don't work everywhere. Does this seem a reasonable set to disable?
Index: Makefile =================================================================== RCS file: /cvs/ports/x11/qt5/Makefile,v retrieving revision 1.48 diff -u -p -r1.48 Makefile --- Makefile 6 Mar 2016 11:56:41 -0000 1.48 +++ Makefile 16 Mar 2016 09:33:26 -0000 @@ -4,6 +4,7 @@ SHARED_ONLY = Yes ONLY_FOR_ARCHS = ${GCC4_ARCHS} VERSION = 5.5.1 +REVISION = 0 ENGINIO_VERSION = 1.2.1 DISTNAME = qt-everywhere-opensource-src-${VERSION} @@ -299,6 +300,15 @@ CONFIGURE_ENV = MAKE=make \ .if ${MACHINE_ARCH} == "powerpc" CONFIGURE_ENV += LDFLAGS="-Wl,--relax" .endif + +.if ${MACHINE_ARCH} == "amd64" || ${MACHINE_ARCH} == "i386" +CONFIGURE_ARGS += -no-ssse3 -no-sse4.1 -no-sse4.2 -no-avx -no-avx2 +.endif + +.if ${MACHINE_ARCH} == "i386" +CONFIGURE_ARGS += -no-sse2 -no-sse3 +.endif + .include <bsd.port.arch.mk> # QtWebkit (at least, maybe others) plays dirty games with inter-target