[Bug-time] time-1.8: building with gcc7 and --enable-gcc-warnings fails

[Jim Meyering]

Hi Assaf,
Thanks a lot for reviving GNU time and for making a new release.
Sorry I didn't see this sooner:
...
src/time.c: In function 'getargs':
src/time.c:664:4: warning: this statement may fall through
[-Wimplicit-fallthrough=]
    usage (EXIT_SUCCESS);
    ^~~~~~~~~~~~~~~~~~~~
src/time.c:665:2: note: here
  case 'o':
  ^~~~