This does not have any effect on Meson's behavior itself, since "meson test"
always rebuilds everything (that is one reason why we are not using it...).
However, mtest2make can use this information to do a selective rebuild
for the requested suite.

Cc: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>