[Bug libstdc++/69450] [6 Regression] libstdc++-v3/include/math.h:66:1 2: error: 'constexpr bool std::isnan(double)' conflicts with a previous declaration

[danglin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69450

--- Comment #1 from John David Anglin <danglin at gcc dot gnu.org> ---
Think the declaration for isnan in include-fixed/math.h should be deleted.
It's an XOPEN extension and conflicts with macro implementation.