Fix custom version file include

Marlin/src/core/macros.h

@@ -21,6 +21,10 @@
  */
 #pragma once
 
+#if !defined(__has_include)
+  #define __has_include(...) 1
+#endif
+
 #define ABCE 4
 #define XYZE 4
 #define ABC  3

Marlin/src/inc/MarlinConfigPre.h

@@ -37,12 +37,8 @@
 #include "../../Configuration.h"
 
 #ifdef CUSTOM_VERSION_FILE
-  #if defined(__has_include)
+  #if __has_include(STRINGIFY(../../CUSTOM_VERSION_FILE))
-    #if __has_include(XSTR(../../CUSTOM_VERSION_FILE))
+    #include STRINGIFY(../../CUSTOM_VERSION_FILE)
-      #include XSTR(../../CUSTOM_VERSION_FILE)
-    #endif
-  #else
-    #include XSTR(../../CUSTOM_VERSION_FILE)
   #endif
 #endif