[CMake] multiple directories in one variable

[Ilja Golshtein]

Hello!

I use a product which (depending on installation type) can keep headers in several directories.

What is the best way to specify these directories?

Do I have better option than variables EXTERNAL_PRODUCT_INCLUDE_1 EXTERNAL_PRODUCT_INCLUDE_2 ...
listed as
include_directories(EXTERNAL_PRODUCT_INCLUDE_1 EXTERNAL_PRODUCT_INCLUDE_2) ?

Ideally I want to write -DEXTERNAL_PRODUCT_INCLUDE="dir1 dir2 dir3" cmake-time, but it does not work.

Thanks.

-- 
Best regards,
Ilja Golshtein.