The full command-line option is /ENVIRONMENT=[NO]FLOAT.

    Controls whether the assembler generates floating-point
    instructions when optimizing code and performing code-label
    alignment.

    Currently, the only floating-point instruction generated by
    the assembler during optimization and alignment processing
    is FNOP, the floating-point no-operation instruction. If you
    specify /ENVIRONMENT=NOFLOAT, the assembler does not generate any
    floating-point instructions as part of optimization and alignment
    processing. Floating-point instructions that you specify in your
    source program are unaffected.