CMake: Use COPYONLY instead of @ONLY

I don't know what happened back in 2009 when I wrote this,
but it seems I used the wrong option. These files should
not have any variable substitution done to them.

CMake/Misc.cmake

@@ -4,7 +4,7 @@ include(CheckCXXCompilerFlag)
 function(flatify target headers)
     foreach(header ${headers})
         get_filename_component(tgt ${header} NAME)
-        configure_file(${header} ${target}/${tgt} @ONLY)
+        configure_file(${header} ${target}/${tgt} COPYONLY)
     endforeach(header ${headers})
 endfunction()
 

CMakeLists.txt

@@ -92,7 +92,7 @@ if (NOT HAVE_STATVFS)
   if (NOT HAVE_VFS_H AND NOT HAVE_MOUNT_H)
     message(FATAL_ERROR "Can find neither statvfs() nor statfs()")
   endif()
-  configure_file(CMake/statvfs.h.in ${PROJECT_BINARY_DIR}/include/statvfs.h @ONLY)
+  configure_file(CMake/statvfs.h.in ${PROJECT_BINARY_DIR}/include/statvfs.h COPYONLY)
 endif()
 
 CHECK_STRUCT_HAS_MEMBER("struct statfs" f_type sys/vfs.h HAVE_STRUCT_STATFS_F_TYPE)