[CMake] Backslashed whitespace in ADD_CUSTOM_COMMAND's ARG expansion

[Eric BOIX]

   Dear CMake users,

I can't seem to be able to use variable expansion within an ADD_CUSTOM_COMMAND.
[I'm using cmake version 2.1.0 on linux].

Here is a small example that shows the encountered difficulty. Assume I define
the following ADD_CUSTOM_COMMAND:

    ADD_CUSTOM_COMMAND(
       OUTPUT    ${CMAKE_CURRENT_BINARY_DIR}/try.cc
       COMMAND   ${OMNIORB4_IDL_COMPILER}
       ARGS      -bcxx -Wba -Wbtp
                 ${CMAKE_CURRENT_SOURCE_DIR}/try.idl
       DEPENDS   ${CMAKE_CURRENT_SOURCE_DIR}/try.idl
       COMMENT   "idl generated code"
     )

Then when executing the make (yes, my platform is Un*x) the expected command
gets properly expanded and invoked i.e. I get
     omniidl -bcxx -Wba -Wbtp [some_path]/try.idl
where the flags of the ARGS argument (-bcxx -Wba -Wbtp) are ok.

NOW, I wish to use a variable to store the flags "-bcxx -Wba -Wbtp"
(because my set of flags is context dependant and I need to define them
 though a bunch of test). Hence I wrote something like:

 SET( IDL_FLAGS "-bcxx -Wba -Wbtp")

 ADD_CUSTOM_COMMAND(
    OUTPUT    ${CMAKE_CURRENT_BINARY_DIR}/try.cc
    COMMAND   ${OMNIORB4_IDL_COMPILER}
    ARGS      ${IDL_FLAGS}                              <---- ONLY CHANGE
              ${CMAKE_CURRENT_SOURCE_DIR}/try.idl
    DEPENDS   ${CMAKE_CURRENT_SOURCE_DIR}/try.idl
    COMMENT   "idl generated code"
  )

Alas when executing the make, the following command is now called
   omniidl -bcxx\ -Wba\ -Wbtp [some_path]/try.idl
i.e. the white-spaces of the IDL_FLAGS variable get BACKSLAHED when the
variable expansion is made (which of course confuses the COMMAND...).

I also tried various combinations of double quotes [and event backslashed
double quotes in deep despair after doing my googling homework with
keywords like white-space, whitespace, backslash ADD_CUSTOM_COMMAND,
ARGS...and going for bug browsing on cmake's bug tracking site], like
     ARGS      "${IDL_FLAGS}"
but without success.

        Any clue about what I'm doing wrong ?
        Thanks,
        Eric Boix.