Add macros for declarative buildsystems of rpm >= 4.20

[fundawang]

In rpm >= 4.201, a new feature Declarative Buildsystem2 will be introduced to simplify spec files. I think we should add support on it.

[eli-schwartz]

This file is maintained by @ignatenkobrain. @DaanDeMeyer @keszybz have demonstrated interest as stakeholders in the past.

Please review (since none of the meson core maintainers know the first thing about rpm, as far as I know :D)

[keszybz]

For related work, see https://src.fedoraproject.org/rpms/pyproject-rpm-macros/pull-request/455.

[eli-schwartz]

$ git --no-pager range-diff --creation-factor=90 origin/master  c07d82dd76f9af01240e8574449bfafb4526451e HEAD

1:  c07d82dd7 ! 1:  0ff4579df Add macros for declarative buildsystems of rpm >= 4.20
    @@ data/macros.meson
              --print-errorlogs \
              %{nil}}
     +
    -+# Macros for declarative buildsystems of rpm >= 4.20
    -+%buildsystem_meson_conf %meson
    -+%buildsystem_meson_build %meson_build
    -+%buildsystem_meson_install %meson_install
    -+%buildsystem_meson_check %meson_test
    ++# Declarative buildsystem, requires RPM 4.20+ to work
    ++# https://rpm-software-management.github.io/rpm/manual/buildsystem.html
    ++%buildsystem_meson_conf() %meson %*
    ++%buildsystem_meson_generate_buildrequires() %{nil}
    ++%buildsystem_meson_build() %meson_build %*
    ++%buildsystem_meson_install() %meson_install %*
    ++%buildsystem_meson_check() %meson_test %*

[jpakkane]

As discussed above, I am one of those people who know nothing about RPM. So is this now ready for merging?

[fundawang]

@pmatilai WDYT?

[bonzini]

LGTM, adding milestone since it doesn't really affect usage of Meson itself.