CI: add workflows for win32 and win64

.github/workflows/build.yml

@@ -34,3 +34,33 @@ jobs:
           sed '/#define _IRR_COMPILE_WITH_OPENGL_/ s|^|//|g' -i include/IrrCompileConfig.h
           cmake .
           make
+
+  win32:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install deps
+        run: |
+          sudo apt-get install cmake g++-mingw-w64-i686 -qyy
+
+      - name: Build
+        run: |
+          ./scripts/ci-build-mingw.sh
+        env:
+          CC: i686-w64-mingw32-gcc
+          CXX: i686-w64-mingw32-g++
+
+  win64:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install deps
+        run: |
+          sudo apt-get install cmake g++-mingw-w64-x86-64 -qyy
+
+      - name: Build
+        run: |
+          ./scripts/ci-build-mingw.sh --64
+        env:
+          CC: x86_64-w64-mingw32-gcc
+          CXX: x86_64-w64-mingw32-g++

scripts/ci-build-mingw.sh

@@ -0,0 +1,36 @@
+#!/bin/bash -e
+
+variant=win32
+[[ "$1" == "--64" ]] && variant=win64
+
+[[ -z "$CC" || -z "$CXX" ]] && exit 255
+
+libjpeg_version=2.0.6
+libpng_version=1.6.37
+zlib_version=1.2.11
+
+mkdir -p libs
+pushd libs
+libs=$PWD
+[ -e libjpeg.zip ] || \
+	wget "http://minetest.kitsunemimi.pw/libjpeg-$libjpeg_version-$variant.zip" -O libjpeg.zip
+[ -e libpng.zip ] || \
+	wget "http://minetest.kitsunemimi.pw/libpng-$libpng_version-$variant.zip" -O libpng.zip
+[ -e zlib.zip ] || \
+	wget "http://minetest.kitsunemimi.pw/zlib-$zlib_version-$variant.zip" -O zlib.zip
+[ -d libjpeg ] || unzip -o libjpeg.zip -d libjpeg
+[ -d libpng ] || unzip -o libpng.zip -d libpng
+[ -d zlib ] || unzip -o zlib.zip -d zlib
+popd
+
+cmake . \
+	-DCMAKE_SYSTEM_NAME=Windows \
+	-DPNG_LIBRARY=$libs/libpng/lib/libpng.dll.a \
+	-DPNG_PNG_INCLUDE_DIR=$libs/libpng/include \
+	-DJPEG_LIBRARY=$libs/libjpeg/lib/libjpeg.dll.a \
+	-DJPEG_INCLUDE_DIR=$libs/libjpeg/include \
+	-DZLIB_LIBRARY=$libs/zlib/lib/libz.dll.a \
+	-DZLIB_INCLUDE_DIR=$libs/zlib/include
+
+make -j$(nproc)
+exit 0