os: switch from "secret features" to non-feature cfgs

This moves basepri and native atomics detection to cfgs (namespaced by
lilos_) instead of fake features. This seems less confusing, since
normally if you see cfg(feature = "foo") in the source, you can expect
to also find a definition of that feature in Cargo.toml... which was not
the case here.

os/build.rs

@@ -3,13 +3,15 @@
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
 fn main() {
-    println!(r#"cargo:rustc-check-cfg=cfg(feature, values("has-basepri", "has-native-rmw"))"#);
+    println!(r#"cargo:rustc-check-cfg=cfg(lilos-has-basepri)"#);
+    println!(r#"cargo:rustc-check-cfg=cfg(lilos-has-native-rmw)"#);
+
     match std::env::var("TARGET").unwrap().as_str() {
         "thumbv7m-none-eabi" | "thumbv7em-none-eabi" | "thumbv7em-none-eabihf" => {
             // Turn on BASEPRI support for interrupt priority filtering.
-            println!("cargo:rustc-cfg=feature=\"has-basepri\"");
+            println!("cargo:rustc-cfg=lilos_has_basepri");
             // Use native atomic RMW operations
-            println!("cargo:rustc-cfg=feature=\"has-native-rmw\"");
+            println!("cargo:rustc-cfg=lilos_has_native_rmw");
         }
         "thumbv6m-none-eabi" => {
             // Don't turn anything on.

os/src/atomic.rs

@@ -80,7 +80,7 @@ macro_rules! impl_atomic_polyfills {
         impl<$($param)?> private::Sealed for $t {}
 
         // Native version
-        #[cfg(feature = "has-native-rmw")]
+        #[cfg(lilos_has_native_rmw)]
         impl<$($param)?> AtomicExt for $t {
             type Value = $v;
 
@@ -113,7 +113,7 @@ macro_rules! impl_atomic_polyfills {
         }
 
         // Non-native version
-        #[cfg(not(feature = "has-native-rmw"))]
+        #[cfg(not(lilos_has_native_rmw))]
         impl<$($param)?> AtomicExt for $t {
             type Value = $v;
 
@@ -186,7 +186,7 @@ impl_atomic_polyfills!(AtomicPtr<T>, *mut T, T);
 macro_rules! impl_atomic_arith_polyfills {
     ($t:ty $(, $param:ident)?) => {
         // Native version
-        #[cfg(feature = "has-native-rmw")]
+        #[cfg(lilos_has_native_rmw)]
         impl<$($param)?> AtomicArithExt for $t {
             fn fetch_add_polyfill(
                 &self,
@@ -214,7 +214,7 @@ macro_rules! impl_atomic_arith_polyfills {
         }
 
         // Non-native version
-        #[cfg(not(feature = "has-native-rmw"))]
+        #[cfg(not(lilos_has_native_rmw))]
         impl<$($param)?> AtomicArithExt for $t {
             fn fetch_add_polyfill(
                 &self,
@@ -262,7 +262,7 @@ impl_atomic_arith_polyfills!(core::sync::atomic::AtomicIsize);
 impl_atomic_arith_polyfills!(AtomicUsize);
 impl_atomic_arith_polyfills!(AtomicU32);
 
-#[cfg(not(feature = "has-native-rmw"))]
+#[cfg(not(lilos_has_native_rmw))]
 #[inline(always)]
 fn rmw_ordering(o: Ordering) -> (Ordering, Ordering) {
     match o {

os/src/exec.rs

@@ -309,7 +309,7 @@ pub enum Interrupts {
     /// adjust this priority in the NVIC.)
     ///
     /// This is not available on ARMv6-M, which lacks the `BASEPRI` feature.
-    #[cfg(feature = "has-basepri")]
+    #[cfg(lilos_has_basepri)]
     Filtered(u8),
 }
 
@@ -332,7 +332,7 @@ impl Interrupts {
 
                 r
             }
-            #[cfg(feature = "has-basepri")]
+            #[cfg(lilos_has_basepri)]
             Interrupts::Filtered(priority) => {
                 let prev = cortex_m::register::basepri::read();
                 cortex_m::register::basepri_max::write(priority);