BuildSystem: Cache results from when pulling the revision-information to avoid regenerating revision.h

(should remove the unneeded rebuilding of some core-files due to that the revision.h file has changed timestamp-wise)

--HG--
branch : trunk

src/genrev/CMakeLists.txt

@@ -10,7 +10,6 @@
 
 # Need to pass old ${CMAKE_BINARY_DIR} as param because its different at build stage
 add_custom_target(revision.h ALL
-  COMMAND ${CMAKE_COMMAND} -E remove ${CMAKE_BINARY_DIR}/revision.h
   COMMAND ${CMAKE_COMMAND} -DBUILDDIR=${CMAKE_BINARY_DIR} -P ${CMAKE_SOURCE_DIR}/cmake/genrev.cmake
   WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
 )