Merge pull request #2032 from schilkp:schilkp/readme_links

PiperOrigin-RevId: 744078993

Integrate LLVM at llvm/llvm-project@537b6541e806

Updates LLVM usage to match
[537b6541e806](https://github.com/llvm/llvm-project/commit/537b6541e806)

PiperOrigin-RevId: 743707094

Automated rollback of commit 584ba1a190ba4e9a873c11eeebdba922ce587a15.

PiperOrigin-RevId: 743322576

Merge pull request #2023 from ericastor:mask_fns

PiperOrigin-RevId: 742866095

Remove codegen specialization for priority selects.

We previously specialized the codegen of priority selects when the selector was never zero. The specialization would call `$error()` if the selector was zero and propagate `X`, the idea being that this form might synthesize to something smaller.

Unfortunately, this specialization causes more headaches than it is worth. The `$error()` call isn't a real assertion, so it could spuriously fire. We also generally prefer to avoid propagating X explicitly.

Benchmarks showed that this specialization didn't give a net benefit on our corpus, so it seems better to avoid the headaches by removing it.

Fixes google/xls#1481.

PiperOrigin-RevId: 742428399

Integrate LLVM at llvm/llvm-project@c0952a931c7d

Updates LLVM usage to match
[c0952a931c7d](https://github.com/llvm/llvm-project/commit/c0952a931c7d)

PiperOrigin-RevId: 741850272

Temporarily disable xls/visualization/ir_viz/app in binary releases.

https://github.com/google/xls/issues/2021

PiperOrigin-RevId: 741680186

Extracted the optimization of merging consecutive PrioritySelect and …

Add test with channel declared in a proc.

The channel results in a FIFO instantiation connected two instantiated procs. No functional change to codegen required.

Also, create a test-only RTL FIFO library out of existing test FIFOs in block_generator_test.

PiperOrigin-RevId: 740921106

Support procs in type_system_v2 to the extent necessary to typecheck …