Add cfg(no_io_statics) to core

Allows disabling the use of a static `AtomicPtr` as an implementation detail of `core::io`, regardless of the platform.

Author: bushrat011899

library/core/Cargo.toml

@@ -40,5 +40,8 @@ check-cfg = [
     'cfg(target_has_reliable_f128)',
     'cfg(target_has_reliable_f128_math)',
     'cfg(llvm_enzyme)',
+    # Prevents use of a static variable for providing platform specific RawOsError
+    # functionality
+    'cfg(no_io_statics)',
 
 ]

library/core/src/io/error.rs

@@ -17,8 +17,14 @@
 )]
 mod repr;
 
-#[cfg_attr(target_has_atomic_load_store = "ptr", path = "error/os_functions_atomic.rs")]
-#[cfg_attr(not(target_has_atomic_load_store = "ptr"), path = "error/os_functions.rs")]
+#[cfg_attr(
+    all(target_has_atomic_load_store = "ptr", not(no_io_statics)),
+    path = "error/os_functions_atomic.rs"
+)]
+#[cfg_attr(
+    not(all(target_has_atomic_load_store = "ptr", not(no_io_statics))),
+    path = "error/os_functions.rs"
+)]
 mod os_functions;
 
 use self::os_functions::{decode_error_kind, format_os_error, is_interrupted, set_functions};