Auto merge of #18189 - JJayet:ios_support, r=larsbergstrom

First step toward iOS Support

This mostly prevents Gaol/sandboxing to be used during compilation.
There are a number of issues with : `expat-sys`, `servo-freetype-sys`, `fontsan`, `heartbeats-simple-sys`, `mozjs_sys`.

Also modified `components/script/dom/navigatorinfo.rs` in order to add iOS.

```rust
#[cfg(target_os = "ios")]
pub fn Platform() -> DOMString {
    DOMString::from("iOS")
}
```

See here for more informations : https://github.com/servo/servo/issues/18154

---

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes partially work on #18154

- [X] These changes do not require tests because it deals with the compile toolchain

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components/constellation/Cargo.toml

@@ -41,5 +41,5 @@ servo_url = {path = "../url"}
 webvr_traits = {path = "../webvr_traits"}
 webrender_api = {git = "https://github.com/servo/webrender", features = ["ipc"]}
 
-[target.'cfg(not(target_os = "windows"))'.dependencies]
+[target.'cfg(all(not(target_os = "windows"), not(target_os = "ios")))'.dependencies]
 gaol = {git = "https://github.com/servo/gaol"}

components/constellation/lib.rs

@@ -16,7 +16,7 @@ extern crate compositing;
 extern crate debugger;
 extern crate devtools_traits;
 extern crate euclid;
-#[cfg(not(target_os = "windows"))]
+#[cfg(all(not(target_os = "windows"), not(target_os = "ios")))]
 extern crate gaol;
 extern crate gfx;
 extern crate gfx_traits;
@@ -46,11 +46,11 @@ mod constellation;
 mod event_loop;
 mod network_listener;
 mod pipeline;
-#[cfg(not(target_os = "windows"))]
+#[cfg(all(not(target_os = "windows"), not(target_os = "ios")))]
 mod sandboxing;
 mod timer_scheduler;
 
 pub use constellation::{Constellation, FromCompositorLogger, FromScriptLogger, InitialConstellationState};
 pub use pipeline::UnprivilegedPipelineContent;
-#[cfg(not(target_os = "windows"))]
+#[cfg(all(not(target_os = "windows"), not(target_os = "ios")))]
 pub use sandboxing::content_process_sandbox_profile;

components/constellation/pipeline.rs

@@ -537,7 +537,7 @@ impl UnprivilegedPipelineContent {
         }
     }
 
-    #[cfg(not(target_os = "windows"))]
+    #[cfg(all(not(target_os = "windows"), not(target_os = "ios")))]
     pub fn spawn_multiprocess(self) -> Result<(), Error> {
         use gaol::sandbox::{self, Sandbox, SandboxMethods};
         use ipc_channel::ipc::IpcOneShotServer;
@@ -585,9 +585,9 @@ impl UnprivilegedPipelineContent {
         Ok(())
     }
 
-    #[cfg(target_os = "windows")]
+    #[cfg(any(target_os = "windows", target_os = "ios"))]
     pub fn spawn_multiprocess(self) -> Result<(), Error> {
-        error!("Multiprocess is not supported on Windows.");
+        error!("Multiprocess is not supported on Windows or iOS.");
         process::exit(1);
     }