Auto merge of #58373 - RalfJung:maybe-uninit, r=gnzlbg

update stdsimd and remove now-unused MaybeUninit::into_inner

That's a huge diff for stdsimd... Cc @gnzlbg @alexcrichton

src/libcore/lib.rs

@@ -124,6 +124,7 @@
 #![feature(adx_target_feature)]
 #![feature(maybe_uninit, maybe_uninit_slice, maybe_uninit_array)]
 #![feature(unrestricted_attribute_tokens)]
+#![feature(external_doc)]
 
 #[prelude_import]
 #[allow(unused)]

src/libcore/mem.rs

@@ -1185,14 +1185,6 @@ impl<T> MaybeUninit<T> {
         ManuallyDrop::into_inner(self.value)
     }
 
-    /// Deprecated alternative to `into_initialized`. Will never get stabilized.
-    /// Exists only to transition stdsimd to `into_initialized`.
-    #[inline(always)]
-    #[allow(unused)]
-    pub(crate) unsafe fn into_inner(self) -> T {
-        self.into_initialized()
-    }
-
     /// Gets a reference to the contained value.
     ///
     /// # Unsafety

src/libstd/Cargo.toml

@@ -47,7 +47,7 @@ fortanix-sgx-abi = { version = "0.3.2", features = ['rustc-dep-of-std'] }
 cc = "1.0"
 
 [features]
-default = ["compiler_builtins_c"]
+default = ["compiler_builtins_c", "std_detect_file_io", "std_detect_dlsym_getauxval"]
 
 backtrace = ["backtrace-sys"]
 panic-unwind = ["panic_unwind"]
@@ -66,3 +66,8 @@ wasm_syscall = []
 # the environment for hooking up some thread-related information like the
 # current thread id and accessing/getting the current thread's TCB
 wasm-bindgen-threads = []
+
+# Enable std_detect default features for stdsimd:
+# https://github.com/rust-lang-nursery/stdsimd/blob/master/crates/std_detect/Cargo.toml
+std_detect_file_io = []
+std_detect_dlsym_getauxval = []