[gimp] gitlab-ci: move to Fedora 31 image for the Win32 CI build.

[Jehan <jehanp src gnome org>]

commit d48dcc125272b263404851a399b5f51543f4a959
Author: Jehan <jehan girinstud io>
Date:   Sun Nov 24 15:55:51 2019 +0100

    gitlab-ci: move to Fedora 31 image for the Win32 CI build.

 .gitlab-ci.yml                                   | 6 +++---
 build/windows/crossbuild-gitlab-ci/build-deps.sh | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 7bb6a48962..8c12038ac5 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -138,7 +138,7 @@ gimp-meson:
     # - ninja test
 
 deps-x86_64-w64-mingw32:
-  image: fedora:30
+  image: fedora:31
   stage: dependencies
   variables:
     XDG_CACHE_HOME: "$CI_PROJECT_DIR/.cache/"
@@ -195,7 +195,7 @@ deps-x86_64-w64-mingw32:
       - _deps/
 
 gimp-x86_64-w64-mingw32-meson:
-  image: fedora:30
+  image: fedora:31
   stage: gimp
   dependencies:
     - deps-x86_64-w64-mingw32
@@ -220,7 +220,7 @@ gimp-x86_64-w64-mingw32-meson:
         libtool
         libxslt
         make
-        python2
+        python3
         mingw64-gcc
         mingw64-gcc-c++
         mingw64-binutils
diff --git a/build/windows/crossbuild-gitlab-ci/build-deps.sh 
b/build/windows/crossbuild-gitlab-ci/build-deps.sh
index 4958eabfcb..34f2dfebf7 100644
--- a/build/windows/crossbuild-gitlab-ci/build-deps.sh
+++ b/build/windows/crossbuild-gitlab-ci/build-deps.sh
@@ -68,6 +68,11 @@ crossroad meson _build && ninja -C _build install || exit 1
 crossroad mask glib
 cd ..
 
+# Fix a bug in Mingw-w64 headers when building with strict
+# C90-compliance.
+# See my commit fb232993 in mingw-w64-mingw-w64 repository.
+sed -i 's%^//\(.*\)$%/*\1 */%' $CROSSROAD_PREFIX/include/stdlib.h
+
 # Pango (available in crossroad but too old)
 
 crossroad install harfbuzz && \