rework langinfo code for ABI compat and for use by time code

[musl] / src / math / logbl.c

#include "libm.h"
#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double logbl(long double x)
{
        return logb(x);
}
#else
long double logbl(long double x)
{
        if (!isfinite(x))
                return x * x;
        if (x == 0)
                return -1/(x+0);
        return ilogbl(x);
}
#endif