[gimp] meson: add a big fat "experimental" warning at end of meson configure.

[Jehan <jehanp src gnome org>]

commit fb0ea1362615903d2b2ed1f212b74b764b8f836a
Author: Jehan <jehan girinstud io>
Date:   Mon Oct 14 18:35:57 2019 +0200

    meson: add a big fat "experimental" warning at end of meson configure.
    
    It should be clear that the autotools build is still the officially
    mandated one for all finale builds (i.e. packaging). Our meson builds
    still have bugs (some we know of and are trying to fix, others that we
    will probably discover soon) so packagers should be well aware that they
    should not use meson (though we highly encourage it for developers so
    that bugs can be found).
    
    Adding this warning as someone was asking on a bug report whether
    autotools were still being supported (while it's the opposite: meson is
    still not officially stable and autotools is still our main build
    system).

 meson.build | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/meson.build b/meson.build
index e82e17bf13..1d3bea49b8 100644
--- a/meson.build
+++ b/meson.build
@@ -1694,3 +1694,12 @@ if warnings.length() > 0
     warning(warning)
   endforeach
 endif
+
+warning('''
+
+        MESON BUILD IS STILL EXPERIMENTAL!
+
+        we encourage usage of meson if you want to test and
+        report bugs. Yet if you are a packager, DO NOT USE
+        meson until we fix all known issues and bugs.
+        ''')