ci: Add a MinGW Docker image

The Fedora image we use contains MinGW bits that ought to go into
their own Docker container. This avoids having a massive Docker image
that gloms everything and is harder to update.

While we're splitting off, we can also update to Fedora 29, as we can
rely on Fedora packagers doing their job and ensuring that the MinGW
cross-compilation toolchain still works.

.gitlab-ci/mingw.Dockerfile

@@ -0,0 +1,70 @@
+FROM fedora:29
+
+RUN dnf -y install \
+    bindfs \
+    clang \
+    clang-analyzer \
+    desktop-file-utils \
+    elfutils-libelf-devel \
+    findutils \
+    fuse \
+    gamin-devel \
+    gcc \
+    gcc-c++ \
+    gettext \
+    git \
+    glibc-devel \
+    glibc-headers \
+    glibc-langpack-de \
+    glibc-langpack-el \
+    glibc-langpack-el \
+    glibc-langpack-en \
+    glibc-langpack-es \
+    glibc-langpack-es \
+    glibc-langpack-fa \
+    glibc-langpack-fr \
+    glibc-langpack-hr \
+    glibc-langpack-ja \
+    glibc-langpack-lt \
+    glibc-langpack-pl \
+    glibc-langpack-ru \
+    glibc-langpack-tr \
+    gtk-doc \
+    itstool \
+    lcov \
+    libattr-devel \
+    libffi-devel \
+    libmount-devel \
+    libselinux-devel \
+    libxslt \
+    mingw64-gcc \
+    mingw64-gcc-c++ \
+    mingw64-gettext \
+    mingw64-libffi \
+    mingw64-zlib \
+    ncurses-compat-libs \
+    ninja-build \
+    pcre-devel \
+    python3 \
+    python3-pip \
+    python3-wheel \
+    systemtap-sdt-devel \
+    unzip \
+    wget \
+    xz \
+    zlib-devel \
+ && dnf clean all
+
+WORKDIR /opt
+COPY cross_file_mingw64.txt /opt
+
+RUN pip3 install meson==0.48.0
+
+ARG HOST_USER_ID=5555
+ENV HOST_USER_ID ${HOST_USER_ID}
+RUN useradd -u $HOST_USER_ID -ms /bin/bash user
+
+USER user
+WORKDIR /home/user
+
+ENV LANG C.UTF-8