[gimp/wip/Jehan/fix-win-CI] build: fix json-c cross-build for Windows.

[Jehan <jehanp src gnome org>]

commit ba3341b30281f0291025b19b1ab5e4d7450afae4
Author: Jehan <jehan girinstud io>
Date:   Sun Mar 15 23:50:38 2020 +0100

    build: fix json-c cross-build for Windows.
    
    I submitted a patch upstream:
    https://github.com/json-c/json-c/pull/556
    
    For the time being, I disable some warnings to at least have a working
    CI.

 build/windows/crossbuild-gitlab-ci/build-deps.sh | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/build/windows/crossbuild-gitlab-ci/build-deps.sh 
b/build/windows/crossbuild-gitlab-ci/build-deps.sh
index 34f2dfebf7..69cded67ec 100644
--- a/build/windows/crossbuild-gitlab-ci/build-deps.sh
+++ b/build/windows/crossbuild-gitlab-ci/build-deps.sh
@@ -35,9 +35,12 @@ cd ..
 
 # json-c
 
+# TODO: implicit-fallthrough and no-return-type warnings must be
+# reenabled once the following patch has been merged into json-c source:
+# https://github.com/json-c/json-c/pull/556
 git clone --depth 1 https://github.com/json-c/json-c.git && \
 mkdir json-c/_build && cd json-c/_build && \
-CFLAGS="-Wno-expansion-to-defined" crossroad ../configure && make install || exit 1
+CFLAGS="-Wno-expansion-to-defined -Wimplicit-fallthrough=0 -Wno-return-type" crossroad ../configure && make 
install || exit 1
 cd ../..
 
 # libmypaint