[CMake] override variable in macro

[Bill Hoffman]

Juan Sanchez wrote:
> I would argue that the following snippet of code should either print
> "CAT" twice or die.  Unfortunately it first prints "DOG" and then "CAT".
>
> Thanks,
>
> Juan
>
> MACRO(FOO BAR)
>   SET (BAR "CAT")
>   MESSAGE("${BAR}")
> ENDMACRO(FOO)
>
> FOO(DOG)
> MESSAGE("${BAR}")
>
>   
So, expand the macro and you get:

SET(BAR "CAT")   # text in a macro is just text, BAR is just more text
MESSAGE("DOG")  # ${BAR} is replaced by DOG sort of like a cpp macro
MESSAGE(${BAR})  # now we print BAR which was set to CAT in the macro

-Bill