Update autocargo-generated cxx dependencies for backtrace_ffi

Summary:
Merge conflict between these 2 diffs:

- {D102213373}
- {D102189200}

overriding_review_checks_triggers_an_audit_and_retroactive_review
Oncall Short Name: rust_foundation

Differential Revision: D104061217

fbshipit-source-id: 8fd01999f64458ee5e1f1affb41f2ea3ae0a4d25

Author: David Tolnay

eden/fs/rust/backtrace_ffi/Cargo.toml

@@ -9,4 +9,4 @@ license = "GPLv2+"
 
 [dependencies]
 backtrace = "0.3"
-cxx = "1.0.119"
+cxx = "1.0.194"