[llvm] [RISCV] Add branch folding before branch relaxation (PR #134760)

[Mikhail R. Gadelha via llvm-commits]

mikhailramalho wrote:

Results from the latest version: https://lnt.lukelau.me/db_default/v4/nts/437?show_delta=yes&show_previous=yes&show_stddev=yes&show_mad=yes&show_all=yes&show_all_samples=yes&show_sample_counts=yes&show_small_diff=yes&num_comparison_runs=0&test_filter=&test_min_value_filter=&aggregation_fn=min&MW_confidence_lv=0.05&compare_to=435&submit=Update

It shows an improvement on mcf and omnetpp, but I believe it's the usual variance of these benchmarks, not the result of the patch.

There is a considerably smaller code size change, but it's still there.

There is a slight reduction in the dynamic instruction count. Blender is not included since it keeps timing out on qemu for me, on both main and the PR branch:
```
Benchmark                       DirA            DirB   Diff (%)
============================================================
500.perlbench_r         165826196163    165450563224     -0.23%
502.gcc_r               219399420992    219237589152     -0.07%
505.mcf_r               156797058570    156780899014     -0.01%
508.namd_r              217322414517    217321947075     -0.00%
510.parest_r            143264868783    143229146094     -0.02%
511.povray_r             30514993260     30514218533     -0.00%
519.lbm_r                95279677706     95279677700     -0.00%
520.omnetpp_r           141462225575    141465993056      0.00%
523.xalancbmk_r         282306179987    282303679984     -0.00%
525.x264_r              183580253185    183577348789     -0.00%
531.deepsjeng_r         350577788862    350508921370     -0.02%
538.imagick_r           238460281807    238460282041      0.00%
541.leela_r             405842310517    405842154288     -0.00%
544.nab_r               396838566662    396837264561     -0.00%
557.xz_r                124382811159    124223819665     -0.13%
``` 


https://github.com/llvm/llvm-project/pull/134760