Move the XTest check to cmake

Where the ifdef was checked, the alternative was a compiler error. We can
shortcut that process and just fail in cmake where the header is not found.

CMakeLists.txt

@@ -200,6 +200,10 @@ if (UNIX)
             set (HAVE_DPMS_PROTOTYPES 1)
         endif()
 
+        if (NOT HAVE_X11_EXTENSIONS_XTEST_H)
+            message (FATAL_ERROR "Missing header: X11/extensions/XTest.h")
+        endif()
+
         if (NOT HAVE_X11_XKBLIB_H)
             message (FATAL_ERROR "Missing header: " ${XKBlib})
         endif()

res/config.h.in

@@ -115,9 +115,6 @@
 /* Define to 1 if you have the <X11/extensions/XKBstr.h> header file. */
 #cmakedefine HAVE_X11_EXTENSIONS_XKBSTR_H ${HAVE_X11_EXTENSIONS_XKBSTR_H}
 
-/* Define to 1 if you have the <X11/extensions/XTest.h> header file. */
-#cmakedefine HAVE_X11_EXTENSIONS_XTEST_H ${HAVE_X11_EXTENSIONS_XTEST_H}
-
 /* Define to 1 if you have the <X11/XKBlib.h> header file. */
 #cmakedefine HAVE_X11_XKBLIB_H ${HAVE_X11_XKBLIB_H}
 

src/lib/platform/IXWindowsImpl.h

@@ -13,11 +13,7 @@
 #	include <X11/extensions/dpms.h>
      }
 #endif
-#if HAVE_X11_EXTENSIONS_XTEST_H
-#	include <X11/extensions/XTest.h>
-#else
-#	error The XTest extension is required to build barrier
-#endif
+#include <X11/extensions/XTest.h>
 #if HAVE_X11_EXTENSIONS_XINERAMA_H
      // Xinerama.h may lack extern "C" for inclusion by C++
      extern "C" {

src/lib/platform/XWindowsKeyState.h

@@ -24,11 +24,7 @@
 #include "XWindowsImpl.h"
 
 #include <X11/Xlib.h>
-#if HAVE_X11_EXTENSIONS_XTEST_H
-#    include <X11/extensions/XTest.h>
-#else
-#    error The XTest extension is required to build barrier
-#endif
+#include <X11/extensions/XTest.h>
 #if HAVE_XKB_EXTENSION
 #    include <X11/extensions/XKBstr.h>
 #endif

src/lib/platform/XWindowsScreenSaver.cpp

@@ -26,11 +26,7 @@
 #include "base/TMethodEventJob.h"
 
 #include <X11/Xatom.h>
-#if HAVE_X11_EXTENSIONS_XTEST_H
-#    include <X11/extensions/XTest.h>
-#else
-#    error The XTest extension is required to build barrier
-#endif
+#include <X11/extensions/XTest.h>
 #if HAVE_X11_EXTENSIONS_DPMS_H
 extern "C" {
 #    include <X11/Xmd.h>