We've had some recurring problems debugging statically linked executables
using libthread_db; this patch is the first of several fixes for that.
This doesn't do much; it just splits the check out from the new_objfile
hook, and calls it from target_post_attach and target_post_startup_inferior
in the Linux native target.
Earlier versions of this patch used an observer instead, which was silly
of me; we only want to do this when we're sitting on top of the Linux
native target, not when we're on top of e.g. the remote target. This
mostly fixes the not-enabling-libthread_db-when-we-should-be class of
problems; there's still one gross hack in remote.c which avoids
calling the new objfile hook for remote targets, but that's a mess
for another day.
Any comments? Otherwise, I'll commit this in a few days. It handles
LinuxThreads, but NPTL needs a little push (coming up next).