Improve symbol lookup for backtraces when debug info not present

We had all the info we were just not using it. Also adjusts the OS X
sigdie_handler to the same thing as the linux one (i.e. look at the
state of the thread before the signal handler rather than including
the signal handler in the backtrace. Fixes #7821
Accidentally commited mac-specific struct
Update link to Arch Linux package

Binary package (both i686 and x86-64 version) has been added to Arch Linux community repo.

Also note, the lastest version could always be obtained through AUR as [julia-git](https://aur.archlinux.org/packages/julia-git/)
Fix #7828
Merge pull request #7827 from autozimu/master

Update link to Arch Linux package
fix #7829 (test for 7810 on 32-bit)
Don't hide jlcall_ functions in C backtraces

It seems a little silly to have these display as unknown frames when
the user explicitly asked to see all the C frames. So, I'm showing them
in that case. Also prints changes the printing of unknown functions for
which we only have an ip.