Adjusting PKG_SUGGESTED_OPTIONS based on arch

[David Brownlee <abs%absd.org@localhost>]

        In some cases it makes sense for slower architectures (m68k, vax
        etc) not not enable certain options by default. A good example
        might be opengl.

        I've just added the following to x11/fltk2/options.mk

            PKG_OPTIONS_VAR=        PKG_OPTIONS.fltk2
            PKG_SUPPORTED_OPTIONS=  opengl
            PKG_SUGGESTED_OPTIONS=

            # Default
            .if ${MACHINE_ARCH} != "m68k" && ${MACHINE_ARCH} != "m68000" && \
                    ${MACHINE_ARCH} != "vax"
            PKG_SUGGESTED_OPTIONS+= opengl
            .endif

        What do people think - is it worth generalising this? Maybe by
        defining a global 'avoid_expensive_options' tunable which can
        default to on for slow architectures?