ports: Add SDL2_mixer port

This allows some ports to use audio :D

I did not port any audio libraries so loading sounds probably doesn't
work :D

ports/SDL2_mixer/build.sh

@@ -0,0 +1,26 @@
+#!/bin/bash ../install.sh
+
+NAME='SDL2_mixer'
+VERSION='2.8.1'
+DOWNLOAD_URL="https://github.com/libsdl-org/SDL_mixer/releases/download/release-$VERSION/SDL2_mixer-$VERSION.tar.gz#cb760211b056bfe44f4a1e180cc7cb201137e4d1572f2002cc1be728efd22660"
+DEPENDENCIES=('SDL2')
+
+configure() {
+	$BANAN_CMAKE --fresh -S . -B build -G Ninja \
+		--toolchain="$BANAN_TOOLCHAIN_DIR/Toolchain.txt" \
+		-DCMAKE_INSTALL_PREFIX='/usr' \
+		-DCMAKE_BUILD_TYPE=Release \
+		-DSDL2MIXER_WAVPACK=OFF \
+		-DSDL2MIXER_MIDI=OFF \
+		-DSDL2MIXER_OPUS=OFF \
+		-DSDL2MIXER_MOD=OFF \
+		 || exit 1
+}
+
+build() {
+	$BANAN_CMAKE --build build || exit 1
+}
+
+install() {
+	$BANAN_CMAKE --install build || exit 1
+}