[gnome-text-editor] build: try with gnu99

[Christian Hergert <chergert src gnome org>]

commit a850d520f0e7759b3aaf97047d095178eaa865aa
Author: Christian Hergert <chergert redhat com>
Date:   Wed Feb 2 21:27:47 2022 -0800

    build: try with gnu99

 .gitlab-ci/test-msvc.bat | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci/test-msvc.bat b/.gitlab-ci/test-msvc.bat
index 81cb547..138c737 100644
--- a/.gitlab-ci/test-msvc.bat
+++ b/.gitlab-ci/test-msvc.bat
@@ -6,7 +6,7 @@ call "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Auxiliar
 
 :: FIXME: make warnings fatal
 pip3 install --upgrade --user meson==0.59.4 || goto :error
-meson -Dwerror=false _build || goto :error
+meson -Dc_std=gnu99 -Dwerror=false _build || goto :error
 ninja -C _build || goto :error
 
 goto :EOF