[PATCH] Enable unwind info in libc-start.c and backtrace.c

[Wilco Dijkstra]

Carlos O'Donell wrote:

> This looks god to me, but I'd like to know what machines you've tested on?
>
> If you tested on aarch64, i386, and arm (v7), then I'd say you've done enough
> to show it work on 64-bit and 32-bit for relevant machines.

I tried it on Arm, AArch64 and x64. I can't get GLIBC to build for i386 or i686 as
whatever magic config I try for 32-bit x86 fails during build (it gets past the config
with a newly built 64-bit GCC and binutils but then gets confused despite -m32 flags).

Wilco