Ignore <Project>_EXACT_VERSION when <Project> was already found
If <Project>_DIR
is defined, there is no need to use the requirement from <Project>_EXACT_VERSION
as the project was already found.
This prevents undefined behavior during the build when upstream projects in a local build change version after an update. The solution is not perfect as we get a warning complaining that the version used during the build does not match the version found.
/cc @sponce
Closes #69 (closed)