[Bug libbacktrace/105240] backtrace_pcinfo leaks memory

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105240

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I thought it would be OK to just use the malloc configuration unconditionally
within libstdc++, but it looks like I need to include the configure checks for
mman.h and use mmap whenever possible. It might even be better to disable the
std::stacktrace feature entirely if mmap isn't available, so we don't get these
malloc leaks.