configure: Use a real header guard for config.h.

configure.ac

@@ -2527,9 +2527,11 @@ esac
 
 dnl **** Generate output files ****
 
-AH_TOP([#ifndef WINE_CROSSTEST
-#define __WINE_CONFIG_H])
-AH_BOTTOM([#endif /* WINE_CROSSTEST */])
+AH_TOP([#ifndef __WINE_CONFIG_H
+#define __WINE_CONFIG_H
+#ifndef WINE_CROSSTEST])
+AH_BOTTOM([#endif /* WINE_CROSSTEST */
+#endif /* __WINE_CONFIG_H */])
 
 AC_CONFIG_COMMANDS([include/stamp-h], [echo timestamp > include/stamp-h])
 

include/config.h.in

 /* include/config.h.in.  Generated from configure.ac by autoheader.  */
 
-#ifndef WINE_CROSSTEST
+#ifndef __WINE_CONFIG_H
 #define __WINE_CONFIG_H
+#ifndef WINE_CROSSTEST
 
 /* Define to a function attribute for Microsoft hotpatch assembly prefix. */
 #undef DECLSPEC_HOTPATCH
@@ -1366,3 +1367,4 @@
 #endif
 
 #endif /* WINE_CROSSTEST */
+#endif /* __WINE_CONFIG_H */