fix documentation build on docs.rs

Instruct the docs.rs documentation builder to pass --cfg
RUTSDOC_disable_feature_compat_errors in RUSTFLAGS when building
documentation, so that builds dont fail because of compile_error!() and
incompatible features [1].

[1]: https://docs.rs/crate/vhost/0.14.0/builds/2193201

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

vhost-user-backend/Cargo.toml

@@ -8,6 +8,10 @@ repository = "https://github.com/rust-vmm/vhost"
 edition = "2021"
 license = "Apache-2.0"
 
+[package.metadata.docs.rs]
+all-features = true
+rustc-args  = ['--cfg RUTSDOC_disable_feature_compat_errors']
+
 [features]
 xen = ["vm-memory/xen", "vhost/xen"]
 postcopy = ["vhost/postcopy", "userfaultfd"]

vhost/Cargo.toml

@@ -12,6 +12,7 @@ edition = "2021"
 
 [package.metadata.docs.rs]
 all-features = true
+rustc-args  = ['--cfg RUTSDOC_disable_feature_compat_errors']
 
 [features]
 default = []