Update cxx fork

Summary: Starting in 1.90.0 a warning is generated for this attribute. This diff copies the [fix from the main cxx repo](dtolnay/cxx#1537)

Reviewed By: dtolnay

Differential Revision: D83271538

fbshipit-source-id: 7e3e4dc853882aa958e7824b2ae4aadfb30cc584

Author: cjlongoria

Cargo.lock

@@ -1,6 +1,6 @@
 [patch.crates-io]
-cxx = { package = "cxx", git = "https://github.com/facebookexperimental/cxx.git", rev = "43f8f85eb1b9d99f10f7228ab679997c484ade69" }
-cxx-build = { package = "cxx-build", git = "https://github.com/facebookexperimental/cxx.git", rev = "43f8f85eb1b9d99f10f7228ab679997c484ade69" }
+cxx = { package = "cxx", git = "https://github.com/facebookexperimental/cxx.git", rev = "870ebbecad0f6be394d4f9fb9bd62b551662651a" }
+cxx-build = { package = "cxx-build", git = "https://github.com/facebookexperimental/cxx.git", rev = "870ebbecad0f6be394d4f9fb9bd62b551662651a" }
 displaydoc = { git = "https://github.com/yaahc/displaydoc", rev = "7dc6e324b1788a6b7fb9f3a1953c512923a3e9f0" }
 quickcheck = { git = "https://github.com/jakoschiko/quickcheck", rev = "6ecdf5bb4b0132ce66670b4d46453aa022ea892c" }