[CMake] Fail target if buildtype is not RelWithDebInfo

[Thomas Sondergaard]

Hi,

I have a custom target that is only enabled on Windows and it only works 
with buildtype RelWithDebInfo. When a developer accidentally runs it 
under a different configuration it doesn't fail in a very obvious way, 
and I'd like to improve that, if possible. I am using the "Visual Studio 
12" (2013) generator.

I imagine something like this

if (WIN32)
     add_custom_target(msi-installer
                       COMMAND if NOT "%CMAKE_BUILD_TYPE%" == 
"RELWITHDEBINFO" (echo "msi-installer only works for build type 
RELWITHDEBINFO" && exit 1)
                       COMMAND ...)
endif()

But that requires the CMAKE_BUILD_TYPE to be in the environment. Is 
there a way to do what I want?

Thanks,
Thomas