[CMake] Remove include directories

[James Bigler]

Is it possible to remove include directories?  I can add them all I want, but 
can I take one out:

INCLUDE_DIRECTORIES(
   ${MY_DIR}
   )

# Add some libraries or other things

REMOVE_INCLUDE_DIRECTORIES(
   ${MY_DIR}
   )

INCLUDE_DIRECTORIES(
   ${MY_OTHER_DIR}
   )

# Add some other libraries

I'm trying to build two copies of the same library, but with different included 
files.

James