Move shared offload globals and define per-kernel globals once

[Sa4dUs]

This PR moves the shared LLVM global variables logic out of the offload intrinsic codegen and generates kernel-specific variables only ont he first call of the intrinsic.

r? @ZuseZ4

[Sa4dUs]

i'm a bit unsure about this location. we could also cache these globals and generate them on the first intrinsic call, but that felt like overloading intrinsic codegen a bit too much

i don't have a strong opinion though, so happy to go with whatever u think is best

[ZuseZ4]

Thanks for the IR and code cleanup, the struct makes it much nicer.
Since this adds some entries to the fullCx, I'll run a

@bors try @rust-timer queue

I don't think it will have any impact, but then again, we thought the same when accidentally causing a regression with autodiff, so let's see.

[rust-bors]

☀️ Try build successful (CI)
Build commit: b120fe9 (b120fe9e9f5cbf9dd3fe1c38c97b3b2d44dd94ee, parent: ed0006a7ba2dc8fabab8ea94d6f843886311b3c7)

[rust-timer]

Finished benchmarking commit (b120fe9): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.1%	[1.1%, 1.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 481.444s -> 482.856s (0.29%)
Artifact size: 390.60 MiB -> 390.60 MiB (-0.00%)