This will allow to check for group options. For example the
-Wformat-security flag depends on -Wformat for GCC.

There is currently no change in behavior.

Before this diff:

mkdir -p before && cd before
cmake -GNinja .. > before.txt

After this diff:

mkdir -p after && cd after
cmake -GNinja .. > after.txt

Then:

diff before/before.txt after/after.txt

should return no difference but the build path.