Attempt to fix fits_si.c on Windows 64.
Attempt to fix fits_si.c on Windows 64.

fredrik-johansson/flint2,wbhart/flint2,jpflori/flint2,dsroche/flint2,jpflori/flint2,wbhart/flint2,dsroche/flint2,fredrik-johansson/flint2,jpflori/flint2,fredrik-johansson/flint2,jpflori/flint2,wbhart/flint2,dsroche/flint2,dsroche/flint2