fix: use irrlicht fork instead of the standard library

Dockerfile

@@ -1,6 +1,7 @@
-FROM alpine:3.11
+FROM alpine:3.13
 
 ENV MINETEST_GAME_VERSION master
+ENV IRRLICHT_VERSION master
 
 COPY .git /usr/src/minetest/.git
 COPY CMakeLists.txt /usr/src/minetest/CMakeLists.txt
@@ -18,7 +19,7 @@ COPY textures /usr/src/minetest/textures
 
 WORKDIR /usr/src/minetest
 
-RUN apk add --no-cache git build-base irrlicht-dev cmake bzip2-dev libpng-dev \
+RUN apk add --no-cache git build-base cmake bzip2-dev libpng-dev \
 		jpeg-dev libxxf86vm-dev mesa-dev sqlite-dev libogg-dev \
 		libvorbis-dev openal-soft-dev curl-dev freetype-dev zlib-dev \
 		gmp-dev jsoncpp-dev postgresql-dev luajit-dev ca-certificates && \
@@ -36,6 +37,14 @@ RUN git clone --recursive https://github.com/jupp0r/prometheus-cpp/ && \
 	make -j2 && \
 	make install
 
+RUN git clone --depth=1 https://github.com/minetest/irrlicht/ -b ${IRRLICHT_VERSION} && \
+	mkdir irrlicht/build && \
+	cd irrlicht/build && \
+	cmake .. \
+		-DCMAKE_BUILD_TYPE=Release && \
+	make -j2 && \
+	make install
+
 WORKDIR /usr/src/minetest
 RUN mkdir build && \
 	cd build && \