[Bug libstdc++/109818] std::trunc() requires a hack after building DJGPP

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109818

--- Comment #21 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh, checking FLT_EVAL_METHOD doesn't work, because that's defined in <float.h>
not <math.h>. So another djgpp-specific "NO_FLOAT_TYPES" macro will be needed.
Sigh.