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

[janezz55 at gmail dot com via Gcc-bugs]

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

--- Comment #9 from Janez Zemva <janezz55 at gmail dot com> ---
I'd also like to mention, that the hack is already present in the c_global
cmath file, but is perhaps in a wrong section of the file, i.e. it is in the
section protected by:

#if defined(__STDCPP_FLOAT64_T__) && defined(_GLIBCXX_DOUBLE_IS_IEEE_BINARY64)

while I can see _GLIBCXX_DOUBLE_IS_IEEE_BINARY64 is defined in c++config.h, I
don't see __STDCPP_FLOAT64_T__ defined anywhere.