nix/ci: add and enable llvm-17

[JakeHillion]

No description provided.

[tyroguru]

I'm approving it but we have some red on a couple of CI checks. Land it if you are happy with them.

[JakeHillion]

Still working on this, need to figure out which failures are for all future revisions and which are for LLVM-17 only. These timeouts in particular seem like an LLVM-17 bug. Will see what 18 does and if they're fine on 18 will skip the tests for 17.

[JakeHillion]

Most of the issues are weird DWARF (old drgn issues mentioned elsewhere) and strange timeouts/linking things. All fine to skip, even though it's not ideal.

The remaining test failure that seems legitimate is OidIntegration.cycles_raw_ptr.

This can be reproduced with JIT logging with: build/test/integration/integration_test_runner --gtest_filter='OidIntegration.cycles_raw_ptr' -P --enable-feature jit-logging. The generated code looks totally fine to my eye and should be following the raw pointers. But the JIT log disagrees:

I20250804 14:25:20.697924 140167335514880 OIDebugger.cpp:267] Outputting JIT logs:
I20250804 14:25:20.697933 140167335514880 OIDebugger.cpp:270] JITLOG: RawNode @00007ffd84314300
I20250804 14:25:20.697937 140167335514880 OIDebugger.cpp:270] JITLOG: value_0 @00007ffd84314300
I20250804 14:25:20.697940 140167335514880 OIDebugger.cpp:270] JITLOG: obj @00007ffd84314300
I20250804 14:25:20.697943 140167335514880 OIDebugger.cpp:270] JITLOG: next_2 @00007ffd84314308
I20250804 14:25:20.697946 140167335514880 OIDebugger.cpp:270] JITLOG: ptr val @0000000000000000
I20250804 14:25:20.697950 140167335514880 OIDebugger.cpp:276] Finished outputting JIT logs.

And treebuilder generates as if there are no next entries, causing the test to fail. Need to spend a bit more time looking at this specific one, I don't know how LLVM-17 could have caused it to fail - maybe the pointer tracking broke?

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