alloc: add unstable cfg features no_rc and no_sync

In Rust for Linux we are using these to make `alloc` a bit
more modular.

A `run-make-fulldeps` test is added for each of them, so that
enabling each of them independently is kept in a compilable state.

Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

alloc/src/lib.rs

@@ -69,6 +69,8 @@
     any(not(feature = "miri-test-libstd"), test, doctest),
     no_global_oom_handling,
     not(no_global_oom_handling),
+    not(no_rc),
+    not(no_sync),
     target_has_atomic = "ptr"
 ))]
 #![no_std]
@@ -223,16 +225,17 @@ mod boxed {
 }
 pub mod borrow;
 pub mod collections;
-#[cfg(not(no_global_oom_handling))]
+#[cfg(all(not(no_rc), not(no_sync), not(no_global_oom_handling)))]
 pub mod ffi;
 pub mod fmt;
+#[cfg(not(no_rc))]
 pub mod rc;
 pub mod slice;
 pub mod str;
 pub mod string;
-#[cfg(target_has_atomic = "ptr")]
+#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
 pub mod sync;
-#[cfg(all(not(no_global_oom_handling), target_has_atomic = "ptr"))]
+#[cfg(all(not(no_global_oom_handling), not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
 pub mod task;
 #[cfg(test)]
 mod tests;