Backwards compatibility with linux pre 2.6.33

[drok]

This series of 3 commits implements:

• Compatibility with kernels older than 2.6.33

  • prior to this, instead of "anon_inode:inotify" linux used "inotify" as filename in /proc/.../fd

• Compatibility with kernels older than 3.8

  • prior to this, the /proc/.../fdinfo/... files did not include a list of inotify watches
  • the "Watches" column is omitted on older kernels

• Compatibility with GCC older than 7.1

  • prior to this, GCC did not support the -Wimplicit-fallthrough= argument

This PR also resolves my concern in https://github.com/mikesart/inotify-info/issues/10#issuecomment-1876581501 about missing info on old kernels

Please merge this PR rather than rebase.

[mikesart]

Thanks Radu!