Delete architecture-specific memchr code in std::sys

Currently all architecture-specific memchr code is only used in
`std::io`. Most of the actual `memchr` capacity exposed to the user
through the slice API is instead implemented in core::slice::memchr.

Hence this commit deletes memchr from std::sys[_common] and replace
calls to it by calls to core::slice::memchr functions. This deletes
(r)memchr from the list of symbols linked to libc.

library/std/src/io/buffered/linewritershim.rs

@@ -1,5 +1,5 @@
 use crate::io::{self, BufWriter, IoSlice, Write};
-use crate::sys_common::memchr;
+use core::slice::memchr;
 
 /// Private helper struct for implementing the line-buffered writing logic.
 /// This shim temporarily wraps a BufWriter, and uses its internals to

library/std/src/io/mod.rs

@@ -304,7 +304,7 @@ use crate::ops::{Deref, DerefMut};
 use crate::slice;
 use crate::str;
 use crate::sys;
-use crate::sys_common::memchr;
+use core::slice::memchr;
 
 #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
 pub use self::buffered::WriterPanicked;

library/std/src/sys/hermit/mod.rs

@@ -27,7 +27,6 @@ pub mod fs;
 pub mod futex;
 #[path = "../unsupported/io.rs"]
 pub mod io;
-pub mod memchr;
 pub mod net;
 pub mod os;
 #[path = "../unix/os_str.rs"]

library/std/src/sys/hermit/os.rs

@@ -9,9 +9,9 @@ use crate::path::{self, PathBuf};
 use crate::str;
 use crate::sync::Mutex;
 use crate::sys::hermit::abi;
-use crate::sys::memchr;
 use crate::sys::unsupported;
 use crate::vec;
+use core::slice::memchr;
 
 pub fn errno() -> i32 {
     0

library/std/src/sys/sgx/mod.rs

@@ -21,7 +21,6 @@ pub mod fd;
 pub mod fs;
 #[path = "../unsupported/io.rs"]
 pub mod io;
-pub mod memchr;
 pub mod net;
 pub mod os;
 #[path = "../unix/os_str.rs"]

library/std/src/sys/solid/mod.rs

@@ -40,7 +40,6 @@ pub mod pipe;
 pub mod process;
 pub mod stdio;
 pub use self::itron::thread;
-pub mod memchr;
 pub mod thread_local_dtor;
 pub mod thread_local_key;
 pub use self::itron::thread_parking;

library/std/src/sys/solid/os.rs

@@ -12,7 +12,8 @@ use crate::sync::{PoisonError, RwLock};
 use crate::sys::common::small_c_string::run_with_cstr;
 use crate::vec;
 
-use super::{error, itron, memchr};
+use super::{error, itron};
+use core::slice::memchr;
 
 // `solid` directly maps `errno`s to μITRON error codes.
 impl itron::error::ItronError {

library/std/src/sys/teeos/mod.rs

@@ -21,8 +21,6 @@ pub mod locks;
 pub mod fs;
 #[path = "../unsupported/io.rs"]
 pub mod io;
-#[path = "../unix/memchr.rs"]
-pub mod memchr;
 pub mod net;
 #[path = "../unsupported/once.rs"]
 pub mod once;
@@ -49,6 +47,8 @@ pub mod time;
 
 use crate::io::ErrorKind;
 
+use core::slice::memchr;
+
 pub fn abort_internal() -> ! {
     unsafe { libc::abort() }
 }

library/std/src/sys/uefi/mod.rs

@@ -57,10 +57,6 @@ use crate::os::uefi;
 use crate::ptr::NonNull;
 use crate::sync::atomic::{AtomicPtr, Ordering};
 
-pub mod memchr {
-    pub use core::slice::memchr::{memchr, memrchr};
-}
-
 static EXIT_BOOT_SERVICE_EVENT: AtomicPtr<crate::ffi::c_void> =
     AtomicPtr::new(crate::ptr::null_mut());
 

library/std/src/sys/unix/mod.rs

@@ -23,7 +23,6 @@ pub mod kernel_copy;
 #[cfg(target_os = "l4re")]
 mod l4re;
 pub mod locks;
-pub mod memchr;
 #[cfg(not(target_os = "l4re"))]
 pub mod net;
 #[cfg(target_os = "l4re")]

library/std/src/sys/unix/os.rs

@@ -21,8 +21,8 @@ use crate::sync::{PoisonError, RwLock};
 use crate::sys::common::small_c_string::{run_path_with_cstr, run_with_cstr};
 use crate::sys::cvt;
 use crate::sys::fd;
-use crate::sys::memchr;
 use crate::vec;
+use core::slice::memchr;
 
 #[cfg(all(target_env = "gnu", not(target_os = "vxworks")))]
 use crate::sys::weak::weak;

library/std/src/sys/unsupported/common.rs

@@ -1,9 +1,5 @@
 use crate::io as std_io;
 
-pub mod memchr {
-    pub use core::slice::memchr::{memchr, memrchr};
-}
-
 // SAFETY: must be called only once during runtime initialization.
 // NOTE: this is not guaranteed to run, for example when Rust code is called externally.
 pub unsafe fn init(_argc: isize, _argv: *const *const u8, _sigpipe: u8) {}

library/std/src/sys/wasi/os.rs

@@ -10,9 +10,9 @@ use crate::os::wasi::prelude::*;
 use crate::path::{self, PathBuf};
 use crate::str;
 use crate::sys::common::small_c_string::{run_path_with_cstr, run_with_cstr};
-use crate::sys::memchr;
 use crate::sys::unsupported;
 use crate::vec;
+use core::slice::memchr;
 
 // Add a few symbols not in upstream `libc` just yet.
 mod libc {

library/std/src/sys/windows/mod.rs

@@ -21,7 +21,6 @@ pub mod fs;
 pub mod handle;
 pub mod io;
 pub mod locks;
-pub mod memchr;
 pub mod net;
 pub mod os;
 pub mod os_str;

library/std/src/sys_common/mod.rs

@@ -24,7 +24,6 @@ pub mod backtrace;
 pub mod fs;
 pub mod io;
 pub mod lazy_box;
-pub mod memchr;
 pub mod once;
 pub mod process;
 pub mod thread;