[CMake] How to run the install step of an ExternalProject when installing the whole project?

[Patrick Boettcher]

Hi list,

I have several externalprojects in my build. Some of them have a quite
complete install-step which I would like to have running when the
parent-build is installed (and not during the compile build of the
parent).

How can I achieve that?

(It is related to the usage of the DESTDIR-variable which is only
present during make install, but not during make)

Thanks in advance for any help,
--
Patrick.