Don't link to xinput and d3dx9.

Both those have runtime loading mechanisms in place. XInput in
particular is rarely distributed on modern Windowses, which caused
unnecessary issues with distributing Allegro games.

Fixes #548.

CMakeLists.txt

@@ -764,10 +764,6 @@ if(WIN32)
         list(APPEND PLATFORM_LIBS ${D3D9_LIBRARIES})
     endif(SUPPORT_D3D)
 
-    if(SUPPORT_XINPUT) 
-      list(APPEND PLATFORM_LIBS ${XINPUT_LIBRARIES})
-    endif(SUPPORT_XINPUT) 
-
     list(APPEND PLATFORM_LIBS ${DINPUT_LIBRARIES})
     if(MINGW AND NOT SHARED)
         list(APPEND PLATFORM_LIBS stdc++)
@@ -810,7 +806,6 @@ endif()
 
 if(SUPPORT_D3D AND WANT_SHADERS_D3D AND D3DX9_FOUND)
     set(ALLEGRO_CFG_SHADER_HLSL 1)
-    list(APPEND PLATFORM_LIBS "${D3DX9_LIBRARY}")
 endif()
 
 # Header files that we need to install.

README_windows.txt

@@ -20,3 +20,16 @@ between displays with different DPIs):
 
 If you for some reason want to opt out of DPI-awareness, utilize the
 application manifests to specify that your app is not DPI-aware.
+
+Runtime DLL Loading
+-------------------
+
+For some of its features, Allegro will look for certain DLLs on the
+system it runs on, but will not explicitly depend them at build time.
+These are as follows:
+
+- msftedit.dll or riched20.dll or riched32.dll - For the native dialog addon.
+
+- d3dx9_${version}.dll - Shader support for the Direct3D backend.
+
+- xinput1_${version}.dll - XInput-based joysticks.