Add stub synth_only headers for cstring, stdlib.h, and tuple.

These headers allow xlscc to parse C++ code that includes <cstring>, <stdlib.h>, and <tuple>, without providing any synthesizable functionality.

PiperOrigin-RevId: 838993421

[codegen 1.5] Implement BlockFinalizationPass, converting ScheduledBl…

Fix OSS build

PiperOrigin-RevId: 836806997

Integrate LLVM at llvm/llvm-project@dea330b38d9c

Updates LLVM usage to match
[dea330b38d9c](https://github.com/llvm/llvm-project/commit/dea330b38d9c)

PiperOrigin-RevId: 836460028

Integrate LLVM at llvm/llvm-project@f2cb5d7a05ba

Updates LLVM usage to match
[f2cb5d7a05ba](https://github.com/llvm/llvm-project/commit/f2cb5d7a05ba)

PiperOrigin-RevId: 835980399

Allow the available area and delay models to be controlled by toolcha…

Minimize flakiness and address actual MSAN mismatches in function_jit…

Make extract_stage respect names and literals.

Previously, unnamed nodes would get different ids and as a result different names. Also, we were cloning literals as params which results in extra delay in cases where the delay model is specialized for literals.

PiperOrigin-RevId: 834477596

[Proc-scoped channels] Make sure channel scope has the right typeinfo…

Rework subroutine calls, direct-in analysis

PiperOrigin-RevId: 833538317