Debug symbols should only be split from finally linked ELFs, not bare
object files. We're already excluding static libraries from splitting
for a similar reason.
The `.gnu_debuglink` sections are also mishandled by LLVM's LLD, which
copies them to its output. For example, this affects Arch Linux's
`/usr/lib/Scrt1.o`.
While we're here (and it changes the code less), also strip GNU LTO data
from bare objects, again for the same reason we're removing it from
static libraries, and apply static library stripping instead of shared
library stripping.
See: https://bugs.gentoo.org/787623
9154600490