misc: advertise auto-compress debug output
misc: advertise auto-compress debug output

By appending .gz to the --debug-file debug output filename, it get automatically
compressed while being written.
Advertise this feature in the --debug-file option help

Change-Id: I7a4696bc288a1f5ad9f47c6f8a2359b06b134d6f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49670
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5