Fix fakesdl headers when SDL directory included

We introduced the `fakesdl` headers back in #18443 so that anyone trying
to use SDL without using `-sUSE_SDL` (or similar) would see an error.

However we only covered the `SDL_xx.h` include case not the
`SDL/SDL_xx.h` use case.

This means that some users were not seeing the errors they should,
including a few of our test cases.

Split out from #26275

Author: sbc100

system/include/fakesdl/SDL/SDL.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_assert.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_atomic.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_audio.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_blendmode.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_clipboard.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_compat.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_config.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_copying.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"

system/include/fakesdl/SDL/SDL_cpuinfo.h

@@ -0,0 +1 @@
+#error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2"