[CMake] can't pipe cl.exe in a custom command

[Brandon Van Every]

I'm trying to grab the cl.exe banner so I can determine the MSVC
version number.  If cl.exe is in the path, then the following works at
a Windows Command Prompt.  This gives a short banner with the VC
version number and copyright.

  cl /? 2> banner.txt

But when I try to do it in a custom command, I can't get it to pipe to
a file.  I see the output go by in the Visual Studio output window,
with 1> prefixed in front of all the lines, and it is saved in
BuildLog.htm, but cbanner.txt has 0 length no matter whether I use >
1> 2> as the pipe.  Does MSVC simply not have a notion of piping or
something?  Do I have to do something MSVC-specific to capture the
output or the error?

IF(MSVC)
ADD_CUSTOM_COMMAND(
  OUTPUT ${CMAKE_BINARY_DIR}/cbanner.txt
  WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
  COMMAND ${CMAKE_C_COMPILER} /? 2> cbanner.txt
)
ADD_CUSTOM_TARGET(cbanner ALL
  DEPENDS ${CMAKE_BINARY_DIR}/cbanner.txt
)
ENDIF(MSVC)


Cheers,
Brandon Van Every