[CMake] CPack components need to be in global scope

[Miguel A. Figueroa-Villanueva]

Hello,

I have filed the following as a feature request
(http://public.kitware.com/Bug/view.php?id=7282). Those interested can
comment...

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Currently the CPack component features depend on some variables such as:

CPACK_COMPONENTS_ALL
CPACK_COMPONENT_${CNAME}_GROUP
...

These variables are typically easier to set at the point where you are
building the component, which might be nested in some hierarchy. For
example, if you have the following hierarchy with a CMakeLists.txt at
each level, then you need to export the variables up at each level.

/
/libs => set(CPACK_COMPONENTS_ALL ${CPACK_COMPONENTS_ALL} PARENT_SCOPE
/libs/any => set(CPACK_COMPONENTS_ALL ${CPACK_COMPONENTS_ALL} any PARENT_SCOPE)

These variables should be collected without the need to be set
globally. Maybe a new command 'add_cpack_component' like the
'add_test' would be useful or having a CPackComponents.cmake file to
collect components, such as tests are collected in
CTestTestfile.cmake.

--Miguel