Tracking issue for wasm32-emscripten ui test failures

[hoodmane]

These are the tests that are failing after #131705:

• abi/numbers-arithmetic/return-float.rs -- adding -Cpanic=abort fixes the failure. The upstream bug report has a C++ reproducer. More reason it would be nice to resolve Support wasm exception handling for Emscripten target #112195.
• async-await/issue-60709.rs -- Emscripten bug that occurs when -lc and -Oz are passed to the linker, can be reproduced with

  echo "fn main(){}" > a.rs
  rustc -Copt-level=z a.rs -o a.js --target=wasm32-unknown-emscripten

• backtrace/dylib-dep.rs -- "Not supported", xfailed in Emscripten: Xfail backtrace ui tests #131776
• backtrace/line-tables-only.rs -- "Not supported", xfailed in Emscripten: Xfail backtrace ui tests #131776
• no_std/no-std-unwind-binary.rs -- compiler says error: lang item required, but not found: eh_catch_typeinfo
• structs-enums/enum-rec/issue-17431-6.rs -- One of the two compiler errors is missing
• test-attrs/test-passed.rs