[libc][NFC] Move 'sleep_briefly' function to common header

Summary:
The llvm#83026 patch has another
use for this function. Additionally add support for the Arm instruction
barrier if this is ever used by other targets.

Author: jhuber6

libc/src/__support/RPC/rpc_util.h

@@ -11,28 +11,15 @@
 
 #include "src/__support/CPP/type_traits.h"
 #include "src/__support/GPU/utils.h"
-#include "src/__support/macros/attributes.h" // LIBC_INLINE
+#include "src/__support/macros/attributes.h"
 #include "src/__support/macros/properties/architectures.h"
+#include "src/__support/threads/sleep.h"
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #include "src/string/memory_utils/inline_memcpy.h"
 
 namespace LIBC_NAMESPACE {
 namespace rpc {
 
-/// Suspend the thread briefly to assist the thread scheduler during busy loops.
-LIBC_INLINE void sleep_briefly() {
-#if defined(LIBC_TARGET_ARCH_IS_NVPTX)
-  if (__nvvm_reflect("__CUDA_ARCH") >= 700)
-    LIBC_INLINE_ASM("nanosleep.u32 64;" ::: "memory");
-#elif defined(LIBC_TARGET_ARCH_IS_AMDGPU)
-  __builtin_amdgcn_s_sleep(2);
-#elif defined(LIBC_TARGET_ARCH_IS_X86)
-  __builtin_ia32_pause();
-#else
-  // Simply do nothing if sleeping isn't supported on this platform.
-#endif
-}
-
 /// Conditional to indicate if this process is running on the GPU.
 LIBC_INLINE constexpr bool is_process_gpu() {
 #if defined(LIBC_TARGET_ARCH_IS_GPU)

libc/src/__support/threads/CMakeLists.txt

@@ -4,6 +4,12 @@ add_header_library(
     mutex_common.h
 )
 
+add_header_library(
+  sleep
+  HDRS
+    sleep.h
+)
+
 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${LIBC_TARGET_OS})
 endif()

libc/src/__support/threads/sleep.h

@@ -0,0 +1,34 @@
+//===-- Utilities for suspending threads ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_SLEEP_H
+#define LLVM_LIBC_SRC___SUPPORT_THREADS_SLEEP_H
+
+#include "src/__support/macros/attributes.h"
+
+namespace LIBC_NAMESPACE {
+
+/// Suspend the thread briefly to assist the thread scheduler during busy loops.
+LIBC_INLINE void sleep_briefly() {
+#if defined(LIBC_TARGET_ARCH_IS_NVPTX)
+  if (__nvvm_reflect("__CUDA_ARCH") >= 700)
+    LIBC_INLINE_ASM("nanosleep.u32 64;" ::: "memory");
+#elif defined(LIBC_TARGET_ARCH_IS_AMDGPU)
+  __builtin_amdgcn_s_sleep(2);
+#elif defined(LIBC_TARGET_ARCH_IS_X86)
+  __builtin_ia32_pause();
+#elif defined(LIBC_TARGET_ARCH_IS_AARCH64)
+  __builtin_arm_isb(0xf);
+#else
+  // Simply do nothing if sleeping isn't supported on this platform.
+#endif
+}
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC___SUPPORT_THREADS_SLEEP_H