Use libepoxy to load in OpenGL functions (#960)

* Use libepoxy to load in OpenGL functions

Prevents having to load them in manually

* Install libepoxy in the CI

* Do not link OpenGL libraries, libepoxy opens them itself

* Add libepoxy to build instructions

.github/workflows/build-macos.yml

@@ -23,7 +23,7 @@ jobs:
       run: |
         rm -rf /usr/local/bin/2to3 # Temporary workaround suggested here - https://github.com/actions/virtual-environments/issues/2322#issuecomment-749211076
         brew update
-        brew install sdl2 qt@5 libslirp libarchive
+        brew install sdl2 qt@5 libslirp libarchive libepoxy
     - name: Create build environment
       run: mkdir ${{runner.workspace}}/build
     - name: Configure

.github/workflows/build-ubuntu-aarch64.yml

@@ -36,7 +36,7 @@ jobs:
         sudo mv /etc/apt/sources.list{.new,}
         sudo apt update
         sudo apt install aptitude
-        sudo aptitude install -y {gcc-10,g++-10,pkg-config}-aarch64-linux-gnu libsdl2-dev:arm64 qtbase5-dev:arm64 libslirp-dev:arm64 libarchive-dev:arm64
+        sudo aptitude install -y {gcc-10,g++-10,pkg-config}-aarch64-linux-gnu libsdl2-dev:arm64 qtbase5-dev:arm64 libslirp-dev:arm64 libarchive-dev:arm64 libepoxy-dev:arm64
     - name: Create build environment
       run: mkdir ${{runner.workspace}}/build
     - name: Configure

.github/workflows/build-ubuntu.yml

@@ -19,7 +19,7 @@ jobs:
       run: |
         sudo rm -f /etc/apt/sources.list.d/dotnetdev.list /etc/apt/sources.list.d/microsoft-prod.list
         sudo apt update
-        sudo apt install cmake libcurl4-gnutls-dev libpcap0.8-dev libsdl2-dev qt5-default libslirp0 libslirp-dev libarchive-dev --allow-downgrades
+        sudo apt install cmake libcurl4-gnutls-dev libpcap0.8-dev libsdl2-dev qt5-default libslirp0 libslirp-dev libarchive-dev libepoxy-dev --allow-downgrades
     - name: Create build environment
       run: mkdir ${{runner.workspace}}/build
     - name: Configure

.github/workflows/build-windows.yml

@@ -24,7 +24,7 @@ jobs:
         choco install msys2
         C:\tools\msys64\usr\bin\bash.exe -lc "pacman -Syuq --noconfirm"
     - name: Install dependencies
-      run: C:\tools\msys64\usr\bin\bash.exe -lc "pacman -Sq --noconfirm git make mingw-w64-x86_64-{cmake,mesa,SDL2,qt5-static,libslirp,libarchive,toolchain}"
+      run: C:\tools\msys64\usr\bin\bash.exe -lc "pacman -Sq --noconfirm git make mingw-w64-x86_64-{cmake,mesa,SDL2,qt5-static,libslirp,libarchive,libepoxy,toolchain}"
     - name: Create build environment
       run: |
         New-Item -ItemType directory -Path ${{runner.workspace}}\melonDS\build