Multiple code fixes and optimizations

Multiple code fixes and optimizations

archive_read_support_format_rar5.c:
  Bitfield int -> signed int

Archive_write_set_format_iso9660.c:
  Bitfield int -> signed int

archive_write_set_format_xar.c:
  Bitfield int -> signed int

archive_write_set_format_7zip.c:
  Bitfield int -> signed int

archive_read_support_format_xar.c
  Remove useless comparsion

archive_read_support_format_rar.c:
  Fix invalid nested loop break.
  Comment out dead code sections.
  Simplify size comparsions of lensymbol and offsymbol.

archive_read_support_filter_uu.c:
  Remove useless comparsions

archive_read_disk_posix.c:
  Remove useless do-while-zero

Found by LGTM.com code analysis