Optionally use system libs (#6094)

* CMake: Make zstd and libzip optionally use system-installed versions

* CMake: Make SDL2 optionally use system version

* CMake: Disable crypto support in bundled libzip

* CMake: Fix bundled SDL build on macOS

.github/workflows/scripts/linux/generate-cmake.sh

@@ -27,6 +27,7 @@ cmake                                       \
 -DOpenGL_GL_PREFERENCE="LEGACY"             \
 -DOPENGL_opengl_LIBRARY=""                  \
 -DXDG_STD=TRUE                              \
+-DUSE_SYSTEM_ZSTD=FALSE                     \
 $ADDITIONAL_CMAKE_ARGS                      \
 -GNinja                                     \
 -B build