Link against SDL2.

- Use MSVC delayed loading on Windows.
- Rely on system libraries for Linux.
- Add libsdl2-dev to Travis.

.travis.yml

@@ -20,6 +20,7 @@ addons:
       - libc++abi-dev
       - libgtk-3-dev
       - libpthread-stubs0-dev
+      - libsdl2-dev
       #- libvulkan1
       #- libvulkan-dev
       - libx11-dev

src/xenia/app/premake5.lua

@@ -71,10 +71,12 @@ project("xenia-app")
       "xcb",
       "X11-xcb",
       "vulkan",
+      "SDL2",
     })
 
   filter("platforms:Windows")
     links({
+      "delayimp", -- This library implements delayed loading on Windows, an MSVC exclusive feature.
       "xenia-apu-xaudio2",
       "xenia-gpu-d3d12",
       "xenia-hid-winkey",
@@ -82,6 +84,11 @@ project("xenia-app")
       "xenia-ui-d3d12",
     })
 
+  filter("platforms:Windows")
+    linkoptions({
+      "/DELAYLOAD:SDL2.dll",  -- SDL is not mandatory on Windows, implementations using native APIs are prefered.
+    })
+
   filter("platforms:Windows")
     -- Only create the .user file if it doesn't already exist.
     local user_file = project_root.."/build/xenia-app.vcxproj.user"