[LoopPass] fixing 'Modification' messages in -debug-pass=Executions for loop passes

Legacy loop pass manager is issuing "Made Modification" message after each Loop Pass
run, however condition for issuing it is accumulated among all the runs.
That leads to confusing 'modification' messages as soon as the first modification is done.

Changing condition to be "current pass made modifications", similar to how
it is being done in all other pass managers.

llvm-svn: 347215