[gimp] Issue #6447: Meson 0.57 build fails.

[Jehan <jehanp src gnome org>]

commit 1e76829989275fe13b55c17fedb68416e8e29ab7
Author: Jehan <jehan girinstud io>
Date:   Sun Feb 21 01:09:53 2021 +0100

    Issue #6447: Meson 0.57 build fails.
    
    No input to use. Also comparing to the autotools build, we were not
    validating against the DTD, hence adding --valid now.
    The other difference was that instead of looping through all XML menu
    files, we are doing the check in one command. After a few tests, it
    seems to work fine this way too and errors are still accurately given
    (telling which file/line has issues), so I leave this difference as-is.
    
    Also this rule is apparently never run (except when explicitly), which
    is why we never discovered this bug until today. It would seem that
    meson 0.57 would now run this rule, which is nice. But we should check
    it is run appropriately (always when any dependencies are changed, never
    when they are not), just like with the autotools build.

 menus/meson.build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/menus/meson.build b/menus/meson.build
index 02b039ed9c..796112fc0d 100644
--- a/menus/meson.build
+++ b/menus/meson.build
@@ -62,9 +62,9 @@ if xmllint.found()
   run_target('validate_menus',
     command: [
       xmllint,
-      '--noout',
+      '--noout', '--valid',
       '--path', meson.current_source_dir(),
-      '@INPUT@', menus_files,
+      menus_files,
     ],
   )
 endif