[CMake] CLEAN_NO_CUSTOM on visual studio

[Andrea Galeazzi]

I noticed that CLEAN_NO_CUSTOM property doesn't work with VS solutions. 
I use this property in order to generate a file containing the 
incremental build number:
add_custom_command(OUTPUT "./BuildNumber.h" COMMAND "myProg" ARGS
                                        "./BuildNumber.h"
                                        DEPENDS ${SOURCES} ${LIB_TO_LINK}
                                        COMMENT "Changing the build number")
 
So I'd like to keep BuildNumber.h even when I make a rebuild-all by VS, 
otherwise myProg has to create a new file with a 0 as build number.
How can I accomplish this task?