Without manual override following problematic code in generated
"configure" script (line 15918):
case "$host_os" in
# Guess yes on glibc systems.
*-gnu* | gnu*) gl_cv_func_signbit="guessing yes" ;;
# Guess yes on native Windows.
mingw*) gl_cv_func_signbit="guessing yes" ;;
# If we don't know, assume the worst.
*) gl_cv_func_signbit="guessing no" ;;
esac
results in declaration conflict with gnulib declaring
int signbit(double)
while system "math.h" providing modern declaration as
constexpr bool signbit(double)
a8040c700a