ANNOUNCE: build system conversion to Meson has landed

[Peter Maydell]

Hi; we've just merged Paolo's patchset that converts the build system
to use Meson. This should mostly be fairly seamless for the average
developer (we hope) but there are a few things to be aware of:

 * you probably want to do a distclean or otherwise do a clean build
   when you first update your git tree to a version of master with Meson
   (especially if you do in-tree builds)
 * out-of-tree builds should continue to work basically normally
 * we have retained compatibility for an "in-tree build" workflow where
   you run configure/make in the source tree, but this is now implemented
   by having configure create a build tree for you under-the-hood
   (but do consider switching to just doing out-of-tree builds)
 * you will need at least GNU Make 3.82 (everybody probably has this
   already unless you're on OSX, in which case install a make from
   homebrew or similar as the Apple-supplied system make is too old)
 * you need the Python 'setuptools' installed
 * we provide meson itself as a submodule, so you don't need to install
   that yourself
 * if you have patches in flight that made build-system related changes
   (eg adding new files) then you'll probably need to update them to
   work with meson; fingers crossed this should be straightforward
 * I will continue to work through the outstanding pullreqs on the
   list, but probably a bunch of them conflict with the meson switchover
   and submaintainers will need to respin them. Sorry about that.
   (I'll work through them and send out the usual "please fix" emails,
   but feel free to actively re-spin before I get to your pullreq if
   you know it's going to need work.)

https://wiki.qemu.org/Features/Meson/Next has a summary of changes
and is worth a quick scan through.

We've tested this as best as we could, but there are probably going
to be a few teething troubles -- please let us know if something
seems to be broken.

thanks
-- PMM