Heads-up: EXCLUDE_FROM_ALL behaviour change in CMake >= 3.14

[Christophe Giboudeaux]

Hi,

Short notice: the EXCLUDE_FROM_ALL behaviour changed in CMake >= 3.14.0 when 
used with add_subdirectories().

EXCLUDE_FROM_ALL now also affects all the targets inside the directory.[1][2]

e.g:
add_subdirectory(foo EXCLUDE_FROM_ALL)

Before:
Targets defined in this directory are not built when running 'make' but can be 
built using 'make -C foo'.

After:
'make -C foo' will not build anything.

Projects concerned by this change:
- kdev-pg-qt, 'make -C examples' does nothing with CMake 3.14
- kooka, 'make -C tools' won't build them

[1] https://cmake.org/cmake/help/v3.14/prop_tgt/EXCLUDE_FROM_ALL.html?
highlight=exclude_from_all
[2] https://cmake.org/cmake/help/v3.14/command/add_subdirectory.html?
highlight=add_subdirectory