[PATCH v2] libstdc++: Improve ostream output for std::stacktrace

[Florian Weimer]

* Jonathan Wakely:

> With this change locations that don't have a source file look like this:
>
>   18# __libc_start_call_main at [0x7fd6568f6574]
>   19# __libc_start_main@GLIBC_2.2.5 at [0x7fd6568f6627]
>   20# _start at [0x4006a4]

Note that DSO name plus offset would be significantly more useful than
just the address, due to ASLR.

Thanks,
Florian