[CMake] OpenWatcom support

[J Decker]

I would like to add something like this, so an option appears in the
gui I can select....

set(CMAKE_WATCOM_WMAKE_TARGET_SYSTEM "" CACHE STRING
      "Set build type (blank is compiler-default)")
set_property(CACHE CMAKE_WATCOM_WMAKE_TARGET_SYSTEM PROPERTY STRINGS
               "" "=NT" "=OS2" "=DOS" "=QNX" )

and then modify the flags to include the build target type... however,
when I change it in the gui, the changes aren't reflected in the new
flags...

SET (CMAKE_CXX_FLAGS_INIT "-w=3 -xs
-bt${CMAKE_WATCOM_WMAKE_TARGET_SYSTEM} -zld")
SET (CMAKE_C_FLAGS_INIT "-w=3 -bt${CMAKE_WATCOM_WMAKE_TARGET_SYSTEM} -zld")

how am I doing this wrong?