contrib/ci.inria.fr/job-1-build-windows.sh: make sure to use mingw tools and not windows ones

contrib/ci.inria.fr/job-1-build-windows.sh

@@ -25,6 +25,8 @@ if test -z "$tarball" ; then
     exit 2
 fi
 
+export PATH=/usr/bin:$PATH
+
 basename=$(basename $tarball .tar.gz)
 test -d $basename && chmod -R u+rwX $basename && rm -rf $basename
 tar xfz $tarball