cmake: set fallback X11_FOUND to false for mac/win builds

Signed-off-by: falkTX <falktx@falktx.com>

Author: falkTX

CMakeLists.txt

@@ -20,9 +20,12 @@ set_property(GLOBAL PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
 find_package(PkgConfig REQUIRED)
 find_package(Qt5 COMPONENTS REQUIRED Core Widgets)
 
-if(NOT (APPLE OR WIN32))
+if(NOT (APPLE OR MINGW OR WIN32))
   find_package(X11 REQUIRED)
   find_package(Qt5 COMPONENTS REQUIRED X11Extras)
+else()
+  set(X11_FOUND FALSE)
+  mark_as_advanced(X11_FOUND)
 endif()
 
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