build-sys: add meson build

The meson build system allows projects to "vendor" dtc easily, thanks to
subproject(). QEMU has recently switched to meson, and adding meson
support to dtc will help to handle the QEMU submodule.

meson rules are arguably simpler to write and maintain than
the hand-crafted/custom Makefile. meson support various backends, and
default build options (including coverage, sanitizer, debug/release
etc, see: https://mesonbuild.com/Builtin-options.html)

Compare to the Makefiles, the same build targets should be built and
installed and the same tests should be run ("meson test" can be provided
extra test arguments for running the equivalent of checkm/checkv).

There is no support EXTRAVERSION/LOCAL_VERSION/CONFIG_LOCALVERSION,
instead the version is simply set with project(), and vcs_tag() is
used for git/dirty version reporting (This is most common and is
hopefully enough. If necessary, configure-time options could be added
for extra versioning.).

libfdt shared library is build following regular naming conventions:
instead of libfdt.so.1 -> libfdt-1.6.0.so (with current build-sys),
libfdt.so.1 -> libfdt.so.1.6.0. I am not sure why the current build
system use an uncommon naming pattern. I also included a libfdt.pc
pkg-config file, as convenience.

Both Linux native build and mingw cross-build pass. CI pass. Tests are
only run on native build.

The current Makefiles are left in-tree, and make/check still work.
Eventually, the Makefiles could be marked as deprecated, to start a
transition period and avoid having to maintain 2 build systems in the
near future.

(run_tests.sh could eventually be replaced by the meson test runner,
which would have several advantages in term of flexibility/features,
but this is left for another day)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20201012073405.1682782-3-marcandre.lureau@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
6 files changed