Fix LLVM trunk API v3 compatibility and require full CI builds

[github-actions]

Build Morok against LLVM trunk 201b446bf71c7c6d37a9bb195ed5e448c5231070. The new pin exposes plugin API v3; rejecting it previously allowed a pure-layer build with no plugin or IR tests, so CI reported successful test steps before failing packaging. Earlier LLVM bumps also failed because the public PassInfoMixin was removed.

• Use RequiredPassInfoMixin for every required Morok pass and migrate removed instruction-insertion, alignment, and opaque-pointer APIs.
• Accept plugin API v2 and v3 from the matching LLVM headers, discard stale cached plugin-header paths when LLVM_DIR changes, and fail configuration when a requested plugin cannot be built.
• Require the plugin and IR test targets in CI and reject empty CTest selections. Add configure-time regressions for supported/unsupported APIs, cache changes, and explicit pure-layer builds.

Post-merge follow-up dcc32b6 fixes the Linux arm64 runtime failure exposed by the full matrix. Caller-keyed dispatch overwrote x19, which LLVM reserves as the frame base for dynamic stack frames. An argument reload consequently read target instruction bytes instead of the Fibonacci index. The AArch64 carrier pool now starts at x20; a focused regression with an aligned dynamic frame and 32 arguments crashes with the old implementation on both Linux and macOS arm64 and passes with the fix.

Post-merge follow-up fe5180a6 fixes the Linux x86 runtime failure. MBA emitted shl i1 ..., 1, which produces LLVM poison and corrupted the arena workload's branch condition. Doubling now yields zero modulo 2 for one-bit operands. An exhaustive regression checks all four Boolean inputs for six operations, one to three layers, and both heuristic settings; it fails on the old pass and passes with the fix. The extra Linux x86 sweep also exposed an invalid syscall fixture: the third argument belongs in rdx, not r10; the fixture now uses the d constraint.

Validation of final master tree 30180306530c1de2481bf2452a45704a473b1513:

• Built LLVM/Clang 24 from the exact new SHA, with ABI-breaking checks disabled as in CI.
• Complete suites on both API-v3 LLVM 24 and API-v2 LLVM 23: 127 CTest entries each, zero failures, with one existing tracerpid_zero_clean skip each.
• All 97 corpus programs compiled clean and obfuscated at high, max.toml, and built-in max; all 95 runtime-selected programs matched clean exit status and normalized output. The two existing runtime exclusions remain asm_context_switch.c and syscall_signals.c.
• Linux arm64: all 93 CI-selected runtime comparisons pass with Ubuntu 24.04/GCC 14 headers and libraries, code generated by the exact pinned LLVM, and the fixed plugin. The existing four platform/runtime exclusions are unchanged.
• Linux x86: all 93 CI-selected runtime comparisons pass under Docker emulation with Debian/GCC 14 headers and libraries and the exact pinned LLVM. The existing four exclusions are unchanged.
• Workflow lint, shell syntax, and whitespace checks passed.

The latest master CI run on fe5180a6 is green on Linux x86_64, Linux arm64, macOS arm64, and Windows x86_64. The CI head, remote master head, and locally tested tree were verified against commit fe5180a6e47cb9a5b0f35a1e2956f21e3363e0ef and tree 30180306530c1de2481bf2452a45704a473b1513. The preceding 2e9928b run was intentionally cancelled after all four LLVM caches were saved to release the final run. The queued dcc32b6 run was intentionally cancelled before any jobs started because the Linux x86 failure required the MBA follow-up. The original Linux x86 cancellation was a hosted-runner acquisition failure: no job steps executed, and GitHub annotated it with “The job was not acquired by Runner of type hosted even after multiple attempts.”