[utils] Allow better identification of matching blocks in update_mca_test_checks.py

[utils] Allow better identification of matching blocks in update_mca_test_checks.py

Insert empty blocks to cause the positions of matching blocks to match
across lists where possible so that later stages of the algorithm can
actually identify them as being identical.

Regenerated all tests with this change.

Differential Revision: https://reviews.llvm.org/D52560

llvm-svn: 343331