X11: Fix CMake not checking for XInput2 headers

Fixes #1480.

CMakeLists.txt

@@ -230,10 +230,16 @@ if (_GLFW_X11)
         message(FATAL_ERROR "The Xcursor headers were not found")
     endif()
 
+    # Check for XInput (modern HID input)
+    if (NOT X11_Xinput_INCLUDE_PATH)
+        message(FATAL_ERROR "The XInput headers were not found")
+    endif()
+
     list(APPEND glfw_INCLUDE_DIRS "${X11_Xrandr_INCLUDE_PATH}"
                                   "${X11_Xinerama_INCLUDE_PATH}"
                                   "${X11_Xkb_INCLUDE_PATH}"
-                                  "${X11_Xcursor_INCLUDE_PATH}")
+                                  "${X11_Xcursor_INCLUDE_PATH}"
+                                  "${X11_Xinput_INCLUDE_PATH}")
 endif()
 
 #--------------------------------------------------------------------

README.md

@@ -120,6 +120,7 @@ information on what to include when reporting a bug.
 
  - Bugfix: The CMake config-file package used an absolute path and was not
    relocatable (#1470)
+ - [X11] Bugfix: The CMake files did not check for the XInput headers (#1480)
 
 
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