Add YieldProcessor implementation for arm (#54829)

src/coreclr/gc/env/gcenv.base.h

@@ -227,15 +227,10 @@ typedef DWORD (WINAPI *PTHREAD_START_ROUTINE)(void* lpThreadParameter);
 
 #endif // defined(__i386__) || defined(__x86_64__)
 
-#ifdef __aarch64__
+#if defined(__arm__) || defined(__aarch64__)
  #define YieldProcessor() asm volatile ("yield")
  #define MemoryBarrier __sync_synchronize
-#endif // __aarch64__
-
-#ifdef __arm__
- #define YieldProcessor()
- #define MemoryBarrier __sync_synchronize
-#endif // __arm__
+#endif // __arm__ || __aarch64__
 
 #endif // _MSC_VER
 

src/coreclr/pal/inc/pal.h

@@ -3582,7 +3582,7 @@ YieldProcessor()
     __asm__ __volatile__(
         "rep\n"
         "nop");
-#elif defined(HOST_ARM64)
+#elif defined(HOST_ARM) || defined(HOST_ARM64)
     __asm__ __volatile__( "yield");
 #else
     return;