* Define OSMINOR & OS_HURD on GNU/Hurd
Add a way to identify GNU/Hurd with b2, and also in the Python support.
* Use /proc/self/exe for executable_path on Hurd
Use the Linux compatibility procfs translator to get the full path of
the current executable.
* Define _GNU_SOURCE on any GNU libc-based OS
Make sure to enable GNU features when building on any OS that uses
GNU libc.
When running in Linux containers the POSIX sysconf can return "too many"
cores or cpus. Instead we prefer using Linux specific sched_getaffinity
there.
This implements partial cpu count information on POSIX systems using
`sysconf` call. This should be the fallback for most Unix like systems
if they don't have a more accurate cpu count API.
This adds a `b2::system_info` class to obtain available information on
system we are running in. Currently provides CPU counts.
And currently only implemented for macOS.
