library/math.m:
    Since code in math.m uses C macros defined in a foreign_decl in float.m,
    math.m needs a foreign_import_module for float, but it did not have one.
    This caused compilation of math.c to math.o to fail *except* with
    intermodule optimization, which gave math.m the required access to
    float.m's internals anyway. The reason we didn't notice is that
    intermodule optimization is the default.