Fix: add name collision detection to FetchContent

When an external component used the same name as a project or
another external component, LazyFetch was misbehaving. This change
makes LazyFetch detect this condition and fail with an error
message.

Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
Change-Id: I8acbf727a30ded5fc9a7114262803615f0cd21d4
1 file changed