c_strto{f,d} ("-nan", NULL) ignore the sign on CentOS 7 and Alpine Linux

[Mohammad-Reza Nabipoor]

Hi.

The following program produces wrong result on CentOS 7.9 (cfarm112),
and on Alpine Linux (cfarm27 and cfarm437):

```c
#include "c-strtod.h"

#include <stdio.h>
#include <stdint.h>

int
main()
{
  union
  {
    float f;
    uint32_t i;
  } u;

  u.f = c_strtof ("-nan", NULL);
  printf ("f:%f x:0x%08x\n", u.f, u.i);
  return 0;
}
```

Output:

  f:nan x:0x7fc00000

Expected output:

  f:-nan x:0xffc00000


You can find a sample package on the mentioned machines on Compile Farm:
  ~mnabipoor/x-0.1.tar.gz


Regards,
Mohammad-Reza Nabipoor