sdl, docs: support pkgconf sdl2-compat via -d sdl_compat (#935)

README.md

@@ -59,6 +59,10 @@ SDL2 is backwards compatible - so anything written against `v2.0.8` can be compi
 against newer versions of the SDL2 library.
 
 Also note that SDL2 **is not** compatible with SDL `v1.x`.
+SDL2 is however compatible with SDL3 through the [`sdl2-compat`](https://github.com/libsdl-org/sdl2-compat) layer.
+Which makes it possible to use the SDL2 API through the SDL3 libraries.
+You can tell `sdl` to use this compatibility layer on systems that support `pkgconfig` by
+passing the compile time flag `-d sdl_compat` when building your `sdl`/SDL2 based V application.
 
 ## Notes on garbage collection and memory issues
 

c/sdl.c.v

@@ -13,7 +13,12 @@ $if !windows {
 		// This is especially useful when building/linking against a
 		// custom compiled version of the libs on *nix.
 		$if !sdl_no_compile_flags ? {
-			#pkgconfig --cflags --libs sdl2
+			$if sdl_compat ? {
+				// Use SDL2 through SDL3 via the compatibility layer
+				#pkgconfig --cflags --libs sdl2_compat
+			} $else {
+				#pkgconfig --cflags --libs sdl2
+			}
 		}
 	}
 } $else {