[Bug libstdc++/81542] Compilation failure with math.h and -D_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81542

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
That macro is for internal use only, you're not allowed to define or undefine
it.