[CMake] order of include dirs

[Brad King]

Alexander Neundorf wrote:
> in KDE we have the problem that e.g. when compiling kdebase the headers 
> in the source dir should be preferred over the installed ones. 
> Usually we would do  
> include_directories( ${KDE4_INCLUDES} ) in the toplevel CMakeLists.txt. 
> When adding more include dirs in CMakeLists.txt in deeper directories, 
> these directories will be appended to the list of include dirs, except 
> when used with the BEFORE keyword. 
> But now we cannot realistically expect that every KDE developer will 
> always remember the BEFORE keyword. 
> So we had two ideas: 
> make the behaviour configurable: 
> # make prepend default: 
> set(CMAKE_INCLUDE_DIRS_APPEND false)  
> # to force appending: 
> include_directories(AFTER dir1 dir2) 
>  
> Problem here: moving cmake files around to another project where this 
> isn't set would change the behaviour. 
>  
> Second idea: 
>  
> include_directories(LAST dir1 dir2) 
>  
> which would have the effect that the listed directories would always be 
> used after all other include dirs specified without the "LAST" keyword. 

I think that will create two ordered lists of include directories
instead of one, which will just be confusing.  I suggest creating a 
kde4_add_indluce_directories macro that adds the BEFORE option:

macro(kde4_add_indluce_directories)
   include_directories(BEFORE ${ARGN})
endmacro(kde4_add_indluce_directories)

-Brad