macOS support; thanks to @MrYadro

This should support ARM64 and x86-64.
-target flag based on information from
https://developer.apple.com/documentation/xcode/building_a_universal_macos_binary#3618377.

.travis.yml

@@ -1,15 +1,44 @@
 language: cpp
-os: linux
 dist: focal
-matrix:
+os: linux
+jobs:
   include:
   - env: TARGET=release_linux-amd64-librw_gl3_glfw-oal
+    os: linux
   - env: TARGET=debug_linux-amd64-librw_gl3_glfw-oal
+    os: linux
+  - env: TARGET=release_macosx-amd64-librw_gl3_glfw-oal PREMAKE5=premake-5.0.0-alpha15
+    compiler: clang
+    os: osx
+    osx_image: xcode12u
+  - env: TARGET=debug_macosx-amd64-librw_gl3_glfw-oal PREMAKE5=premake-5.0.0-alpha15
+    compiler: clang
+    os: osx
+    osx_image: xcode12u
+addons:
+  apt:
+    update: true
+    packages:
+      - linux-libc-dev
+      - libopenal-dev
+      - libglew-dev
+      - libglfw3-dev
+      - libsndfile1-dev
+      - libmpg123-dev
+      - gcc-8-multilib
+      - g++-8-multilib
+  homebrew:
+    packages:
+      - libsndfile
+      - mpg123
+      - glew
+      - glfw
+      - openal-soft
 script:
-  - sudo apt-get update
-  - sudo apt-get -y install linux-libc-dev libopenal-dev libglew-dev libglfw3-dev libsndfile1-dev libmpg123-dev gcc-8-multilib g++-8-multilib
   - mkdir -p "$TRAVIS_BUILD_DIR/build"
   - cd "$TRAVIS_BUILD_DIR"
-  - ./premake5Linux --with-librw gmake2
-  - cd build 
-  - CC=gcc-8 CXX=g++-8 make config=$TARGET -j4 verbose=1
+  - if [ "$TRAVIS_OS_NAME" = linux ]; then ./premake5Linux --with-librw gmake2; fi
+  - if [ "$TRAVIS_OS_NAME" = osx ]; then curl -L -o "${PREMAKE5}.zip" "https://github.com/premake/premake-core/releases/download/v5.0.0-alpha15/${PREMAKE5}-src.zip" && unzip -q "${PREMAKE5}.zip" && cd "$PREMAKE5" && make -f Bootstrap.mak osx && cd .. && "./${PREMAKE5}/bin/release/premake5" --with-librw gmake2; fi
+  - cd build
+  - if [ "$TRAVIS_OS_NAME" = linux ]; then env CC=gcc-8 CXX=g++-8 make config=$TARGET -j4 verbose=1; fi
+  - if [ "$TRAVIS_OS_NAME" = osx ]; then make config=$TARGET -j4 verbose=1; fi