meson: add build-summary

meson: add build-summary

This roughly mirrors what we get from autotools. There's a few
differences, though:

1. The "exec_prefix" output has been dropped. Meson doesn't support
   this, so it makes no sense here.
2. The "llvm-config" output has been dropped. Meson abstracts dependency
   discovery a bit more than our autotools build-system does, so it's
   not easy to get this information as-is.
3. HUD extra stats, SWR archs, Shared/Static libs and CFLAGS / CXXFLAGS /
   LDFLAGS has been dropped. These can be inspected by "meson configure".
4. How we set defines works quite differently in our Meson build-system,
   and the result isn't quite the same. In particular, the DEFINES output
   has been dropped, to avoid having to refactor the code too much.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109326
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Acked-by: Dylan Baker <dylan@pnwbakers.com>