[backend] Add machine_ir_check

The new functions validate that basic blocks are constructed correctly
and properly linked.

Bug: 291127204
Test: mm and berberis_host_tests
Change-Id: Ie66e29d3e1d0310901d98a309e30a69d15358bb4
Merged-In: Ie66e29d3e1d0310901d98a309e30a69d15358bb4
5 files changed