CMake - Workaround set Boost_component_FOUND

CMake - Workaround set Boost_component_FOUND

BuildBoost.cmake (used when we're building the submodule) doesn't
provide parity with FindBoost.cmake (used with system Boost).
Specifically, it doesn't set the _FOUND variables for the various
components, making it hard to depend on finding those features.

Set Boost_<component>_FOUND for all the components we're building in
BuildBoost.cmake to make using these variables possible.

Signed-off-by: Daniel Gryniewicz <dang@redhat.com>
(cherry picked from commit 0f4cb207bb4a9905619894286edd41a89379a747)
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>