Adjust some ui tests re. target-dependent errors
Alternatives to optional error annotations in #140586:
- Continue to ignore target-dependent additional errors in `tests/ui/panic-runtime/{two-panic-runtimes.rs,tests/ui/panic-runtime/want-abort-got-unwind.rs,tests/ui/panic-runtime/want-abort-got-unwind2.rs}` -- but explain why some targets have more errors than others.
- Use `-Cpanic=abort` for `tests/ui/cfg/cfg_false_no_std-2.rs`. In that test, the panic strategy does not matter w.r.t. test intention.
- Adjust FIXMEs in `tests/ui/debuginfo/debuginfo-type-name-layout-ice-94961-2.rs` to track it in #140620.
---
try-job: armhf-gnu
try-job: test-various
try-job: x86_64-msvc-1
try-job: i686-msvc-1
try-job: x86_64-mingw-1
try-job: aarch64-apple
try-job: x86_64-apple-1
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