Add linux32 target

crosstool-ng is set to build gcc targetting -march=i686 (Pentium Pro), as there
is little to no sense to support anything lower than that.

images/base-linux32/Dockerfile

@@ -0,0 +1,68 @@
+ARG GH_REPO=ghcr.io/fwgs/ffmpeg-builds
+FROM $GH_REPO/base:latest
+
+RUN --mount=src=ct-ng-config,dst=/.config \
+    git clone --filter=blob:none https://github.com/crosstool-ng/crosstool-ng.git /ct-ng && cd /ct-ng && \
+    ./bootstrap && \
+    ./configure --enable-local && \
+    make -j$(nproc) && \
+    cp /.config .config && \
+    ./ct-ng build && \
+    cd / && \
+    rm -rf ct-ng
+
+# Prepare "cross" environment to heavily favour static builds
+RUN \
+    find /opt/ct-ng -type l \
+        -and -name '*.so' \
+        -and -not -ipath '*plugin*' \
+        -and -not -name 'libdl.*' \
+        -and -not -name 'libc.*' \
+        -and -not -name 'libm.*' \
+        -and -not -name 'libmvec.*' \
+        -and -not -name 'librt.*' \
+        -and -not -name 'libpthread.*' \
+        -delete && \
+    find /opt/ct-ng \
+        -name 'libdl.a' \
+        -or -name 'libc.a' \
+        -or -name 'libm.a' \
+        -or -name 'libmvec.a' \
+        -or -name 'librt.a' \
+        -or -name 'libpthread.a' \
+        -delete && \
+    mkdir /opt/ffbuild
+
+ENV FFBUILD_TOOLCHAIN=i686-ffbuild-linux-gnu \
+    FFBUILD_RUST_TARGET="i686-unknown-linux-gnu"
+
+#RUN \
+#    rustup default nightly && \
+#    echo "[unstable]\ntarget-applies-to-host = true\nhost-config = true\n" > "$CARGO_HOME"/config.toml && \
+#    echo "[target.$FFBUILD_RUST_TARGET]\nlinker = \"${FFBUILD_TOOLCHAIN}-gcc\"\nar = \"${FFBUILD_TOOLCHAIN}-gcc-ar\"\n" >> "$CARGO_HOME"/config.toml && \
+#    echo "[target.host]\nlinker = \"gcc\"\nar = \"ar\"\n" >> "$CARGO_HOME"/config.toml
+
+ADD toolchain.cmake /toolchain.cmake
+ADD cross.meson /cross.meson
+
+ADD gen-implib.sh /usr/bin/gen-implib
+RUN git clone --filter=blob:none --depth=1 https://github.com/yugr/Implib.so /opt/implib
+
+ENV PATH="/opt/ct-ng/bin:${PATH}" \
+    FFBUILD_TARGET_FLAGS="--pkg-config=pkg-config --cross-prefix=${FFBUILD_TOOLCHAIN}- --arch=i686 --target-os=linux" \
+    FFBUILD_CROSS_PREFIX="${FFBUILD_TOOLCHAIN}-" \
+    FFBUILD_PREFIX=/opt/ffbuild \
+    FFBUILD_CMAKE_TOOLCHAIN=/toolchain.cmake \
+    PKG_CONFIG=pkg-config \
+    PKG_CONFIG_LIBDIR=/opt/ffbuild/lib/pkgconfig:/opt/ffbuild/share/pkgconfig \
+    CC="${FFBUILD_TOOLCHAIN}-gcc" \
+    CXX="${FFBUILD_TOOLCHAIN}-g++" \
+    LD="${FFBUILD_TOOLCHAIN}-ld" \
+    AR="${FFBUILD_TOOLCHAIN}-gcc-ar" \
+    RANLIB="${FFBUILD_TOOLCHAIN}-gcc-ranlib" \
+    NM="${FFBUILD_TOOLCHAIN}-gcc-nm" \
+    CFLAGS="-static-libgcc -static-libstdc++ -I/opt/ffbuild/include -O2 -pipe -fPIC -DPIC -D_FORTIFY_SOURCE=2 -fstack-protector-strong -fstack-clash-protection -pthread" \
+    CXXFLAGS="-static-libgcc -static-libstdc++ -I/opt/ffbuild/include -O2 -pipe -fPIC -DPIC -D_FORTIFY_SOURCE=2 -fstack-protector-strong -fstack-clash-protection -pthread" \
+    LDFLAGS="-static-libgcc -static-libstdc++ -L/opt/ffbuild/lib -O2 -pipe -fstack-protector-strong -fstack-clash-protection -Wl,-z,relro,-z,now -pthread -lm" \
+    STAGE_CFLAGS="-fvisibility=hidden -fno-semantic-interposition" \
+    STAGE_CXXFLAGS="-fvisibility=hidden -fno-semantic-interposition"

images/base-linux32/cross.meson

@@ -0,0 +1,13 @@
+[binaries]
+c = 'i686-ffbuild-linux-gnu-gcc'
+cpp = 'i686-ffbuild-linux-gnu-g++'
+ld = 'i686-ffbuild-linux-gnu-ld'
+ar = 'i686-ffbuild-linux-gnu-gcc-ar'
+ranlib = 'i686-ffbuild-linux-gnu-gcc-ranlib'
+strip = 'i686-ffbuild-linux-gnu-strip'
+
+[host_machine]
+system = 'linux'
+cpu_family = 'x86'
+cpu = 'i686'
+endian = 'little'