[llvm] [MISched][RISCV] Add anti-dependency breaking to PostMachineScheduler (PR #221984)

[Luke Lau via llvm-commits]

lukel97 wrote:

Performance diff seems fine: https://lnt.lukelau.me/db_default/v4/nts/1642?show_delta=yes&show_previous=yes&show_stddev=yes&show_mad=yes&show_all=yes&show_all_samples=yes&show_sample_counts=yes&num_comparison_runs=0&test_filter=&test_min_value_filter=&aggregation_fn=min&MW_confidence_lv=0.05&compare_to=1643&submit=Update

https://github.com/llvm/llvm-project/pull/221984