Auto merge of #117519 - mj10021:issue-117470-fix, r=<try>

Add cache line size padding to RWLock

Fixing issue #117470, this PR just copies the `cfg_attr` `repr` from the cache padding crate to stop RWLocks from sharing cache lines.

Author: bors

library/std/src/sync/rwlock.rs

@@ -77,6 +77,41 @@ use crate::sys::locks as sys;
 /// [`Mutex`]: super::Mutex
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "RwLock")]
+#[cfg_attr(
+    any(target_arch = "x86_64", target_arch = "aarch64", target_arch = "powerpc64",),
+    repr(align(128))
+)]
+#[cfg_attr(
+    any(
+        target_arch = "arm",
+        target_arch = "mips",
+        target_arch = "mips64",
+        target_arch = "riscv32",
+        target_arch = "riscv64",
+        target_arch = "sparc",
+        target_arch = "hexagon",
+    ),
+    repr(align(32))
+)]
+#[cfg_attr(target_arch = "m68k", repr(align(16)))]
+#[cfg_attr(target_arch = "s390x", repr(align(256)))]
+#[cfg_attr(
+    not(any(
+        target_arch = "x86_64",
+        target_arch = "aarch64",
+        target_arch = "powerpc64",
+        target_arch = "arm",
+        target_arch = "mips",
+        target_arch = "mips64",
+        target_arch = "riscv32",
+        target_arch = "riscv64",
+        target_arch = "sparc",
+        target_arch = "hexagon",
+        target_arch = "m68k",
+        target_arch = "s390x",
+    )),
+    repr(align(64))
+)]
 pub struct RwLock<T: ?Sized> {
     inner: sys::RwLock,
     poison: poison::Flag,