ROOT installation fix: prefix Vc/ for includes

The includes in examples were not adjusted for the different directory
structure. Now the script is much more robust.

Signed-off-by: Matthias Kretz <kretz@kde.org>
less noise: #warning -> comment

It really isn't very useful for a user that compiles the test to see the
warning about the GCC bug all the time. Keep it as a comment in the
code, though.

Signed-off-by: Matthias Kretz <kretz@kde.org>
correct namespace for ROOT and fix inc guards

Signed-off-by: Matthias Kretz <kretz@kde.org>
cmake: adjustments for inside ROOT buildsystem

inside ROOT Vc_INSIDE_ROOT is defined. In that case we need to do some
adjustments for nameing and placing the tests.
Also the libc++ switch is now left alone - the ROOT buildsystem needs to
figure it out.

Signed-off-by: Matthias Kretz <kretz@kde.org>

Conflicts:
	cmake/VcMacros.cmake
	tests/CMakeLists.txt