Rollup merge of #152241 - hoodmane:wasm-unwind-link-cpp-exception, r=alexcrichton

For panic=unwind on Wasm targets, define __cpp_exception tag

Since llvm/llvm-project#159143, llvm no longer weak links the __cpp_exception tag into each object that uses it. They are now defined in compiler-rt. Rust doesn't seem to get them from compiler-rt so llvm decides they need to be imported. This adds them to libunwind.

Same changes applied to compiler-builtins: rust-lang/compiler-builtins#1077

See wasm-bindgen/wasm-bindgen#4938 for a downstream workaround.

cc @sbc100

Author: JonathanBrouwer