I'm compiling an app for a device where the architecture does not support sse beyond sse2, and was wondering is it possible to disable compiling with sse3 instructions from GNU autoconf generated configure scripts? I know you can turn it off in gcc/g++ with mno-sse3 option, but it would be nice if I could turn it off at the configuration level rather than generating a make file and then manually inserting that compiler flag...
Sure. Just set the required flags before calling configure:
$ CFLAGS="-mtune i386" ./configure --enable-this --disable-that ...
You might want to try -march if -mtune does the wrong thing, I haven't tested this lately.