Include debug information in all builds

[jvsalo]

Richard Yao suggested we should make sure that ZoL modules always contain debug info to allow debugging crashes, eg. figuring out line numbers, with gdb. On some build systems this works, but on others (eg. my Debian DKMS) you get

Reading symbols from /lib/modules/3.2.0-4-amd64/updates/dkms/zfs.ko...(no debugging symbols found)...done.
(gdb) list *(arc_read+0x5fe)
No symbol table is loaded.  Use the "file" command.

[behlendorf]

The reason debugging symbols are sometimes available and other times not is because this is managed by the distributions default kernel build options. Distributions such as Debian and Ubuntu strip the symbols by default for kernel modules. On Fedora/EPEL systems the symbols will be stripped but can be installed if needed from the -debuginfo packages.

Unfortunately this isn't something we can do upstream. The various downstream maintainers will need to enable this the right way for their distributions. It will also significantly increase the size of the modules although these days I doubt that's much of a real concern.

[behlendorf]

Will be resolved by #2734.

[behlendorf]

Closing as unnecessary until I hear otherwise.