gh-89640: Restore configure error message on failure to detect float word order (#126569)

Before #126387, if we didn't detect float word order we'd raise the following
configure error:

    Unknown float word ordering. You need to manually preset
    ax_cv_c_float_words_bigendian=no (or yes) according to your system.

This puts it back (except for ARM or WASM, which as hardcoded).