Fix printf-family functions on long double inf

[GabrielRavier]

Cosmopolitan's printf-family functions currently very poorly handle being passed a long double infinity.

For instance, a program such as:

#include <stdio.h>

int main()
{
    printf("%f\n", 1.0 / 0.0);
    printf("%Lf\n", 1.0L / 0.0L);
    printf("%e\n", 1.0 / 0.0);
    printf("%Le\n", 1.0L / 0.0L);
    printf("%g\n", 1.0 / 0.0);
    printf("%Lg\n", 1.0L / 0.0L);
}

will currently output the following:

inf
0.000000[followed by 32763 more zeros]
inf
N.aN0000e-32769
inf
N.aNe-32769

when the correct expected output would be:

inf
inf
inf
inf
inf
inf

This patch fixes this, and adds tests for the behavior.

[jart]

Nice! Thanks!