Add Windows testing

.github/actions/mingw-configure.sh

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+#!/bin/bash
+
+source mingw-env @TRIPLE@
+echo LAST IS: $last
+
+# check if last arg is a path to configure, else use parent
+for last; do true; done
+if test -x "${last}/configure"; then
+  config_path="$last"
+else
+  config_path=".."
+fi
+
+${config_path}/configure \
+  --host=@TRIPLE@ --target=@TRIPLE@ --build="$CHOST" \
+  --prefix=/usr/@TRIPLE@ --libdir=/usr/@TRIPLE@/lib --includedir=/usr/@TRIPLE@/include \
+  --enable-shared --enable-static "$@"

.github/actions/mingw-env.sh

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+#!/bin/sh
+
+_arch=$1
+
+default_mingw_pp_flags="-D_FORTIFY_SOURCE=2"
+default_mingw_compiler_flags="$default_mingw_pp_flags -O2 -pipe -fno-plt -fexceptions --param=ssp-buffer-size=4"
+default_mingw_linker_flags="-Wl,-O1,--sort-common,--as-needed -fstack-protector"
+
+export CPPFLAGS="${MINGW_CPPFLAGS:-$default_mingw_pp_flags $CPPFLAGS}"
+export CFLAGS="${MINGW_CFLAGS:-$default_mingw_compiler_flags $CFLAGS}"
+export CXXFLAGS="${MINGW_CXXFLAGS:-$default_mingw_compiler_flags $CXXFLAGS}"
+export LDFLAGS="${MINGW_LDFLAGS:-$default_mingw_linker_flags $LDFLAGS}"
+
+mingw_prefix=/usr/${_arch}
+export PKG_CONFIG_SYSROOT_DIR="${mingw_prefix}"
+export PKG_CONFIG_LIBDIR="${mingw_prefix}/lib/pkgconfig:${mingw_prefix}/share/pkgconfig"

.github/actions/mingw-w64-libpng-dev.sh

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+#!/bin/sh
+
+# This script was written by ISSOtm while looking at Arch Linux's PKGBUILD for
+# the corresponding package. (And its dependencies)
+# https://aur.archlinux.org/packages/mingw-w64-libpng/
+
+set -e
+
+pngver=1.6.37
+_apngver=$pngver
+_arch="$1"
+
+
+## Install mingw-configure and mingw-env (both build dependencies)
+
+install -m 755 .github/actions/mingw-env.sh /usr/bin/mingw-env
+
+sed "s|@TRIPLE@|${_arch}|g" .github/actions/mingw-configure.sh > ${_arch}-configure
+install -m 755 ${_arch}-configure /usr/bin/
+
+
+## Grab sources and check them
+
+wget http://downloads.sourceforge.net/sourceforge/libpng/libpng-$pngver.tar.xz
+wget http://downloads.sourceforge.net/project/apng/libpng/libpng16/libpng-$_apngver-apng.patch.gz
+sha256sum -c .github/actions/mingw-w64-libpng-dev.sha256sums
+
+## Extract sources
+
+tar -xf libpng-$pngver.tar.xz
+gunzip libpng-$_apngver-apng.patch.gz
+
+
+## Start building!
+
+cd libpng-$pngver
+# Patch in apng support
+patch -p0 ../libpng-$_apngver-apng.patch
+
+mkdir -p build-${_arch}
+cd build-${_arch}
+${_arch}-configure LDFLAGS=-static-libgcc
+make
+make install

.github/actions/mingw-w64-libpng-dev.sha256sums

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+10d9e0cb60e2b387a79b355eb7527c0bee2ed8cbd12cf04417cabc4d6976683c  libpng-1.6.37-apng.patch.gz
+505e70834d35383537b6491e7ae8641f1a4bed1876dbfe361201fc80868d88ca  libpng-1.6.37.tar.xz