timestamp formatting: always use 64-bit for timesstamp formatting.

[tisyang]

Using C99 unsigned long long to format struct timeval's tv_sec and tv_usec, fix incorrect print under some 32bit platform which using time64.

To fix issue #469. It may looks ugly, but straightforward.

[marckleinebudde]

asc2log.c: In function ‘main’:
asc2log.c:438:31: warning: variable ‘tmp_tv’ set but not used [-Wunused-but-set-variable]
  438 |         static struct timeval tmp_tv; /* tmp frame timestamp from ASC file */
      |                               ^~~~~~

[tisyang]

asc2log.c: In function ‘main’:
asc2log.c:438:31: warning: variable ‘tmp_tv’ set but not used [-Wunused-but-set-variable]
  438 |         static struct timeval tmp_tv; /* tmp frame timestamp from ASC file */
      |                               ^~~~~~

It seems that tmp_tv is only used for input check in code, set but not used. I will check again tomorrow and make some change to avoid warning.

[tisyang]

@marckleinebudde source code has been updated to fix compile warning [-Wunused-but-set-variable] about tmp_tv.