libunwind: restore _Unwind_CallPersonality for release LLVM

Nixpkgs builds emscripten with the release LLVM, not the llvm-project
main commit that emsdk pins. Release LLVM (<= 22.x) emits calls to
_Unwind_CallPersonality. llvm-project PR #209282 moved that helper into
libc++abi, renamed to __gxx_wasm_personality_v0. Add the old name back
as a forwarder to the new name. Remove this patch when llvmPackages
reaches LLVM 23.

--- a/system/lib/libunwind/src/Unwind-wasm.c
+++ b/system/lib/libunwind/src/Unwind-wasm.c
@@ -95,4 +95,11 @@
   return 0;
 }
 
+_Unwind_Reason_Code __gxx_wasm_personality_v0(void *exception_ptr);
+
+_LIBUNWIND_EXPORT _Unwind_Reason_Code
+_Unwind_CallPersonality(void *exception_ptr) {
+  return __gxx_wasm_personality_v0(exception_ptr);
+}
+
 #endif // defined(__WASM_EXCEPTIONS__)