Cygwin: testsuite: Fix compilation for arm64

Introduce a cpu_relax.h header to provide architecture-specific
processor idling instructions for the`cancel3` and `cancel5` tests.

Author: thiru-mcw

winsup/testsuite/winsup.api/pthread/cancel3.c

@@ -40,6 +40,7 @@
  */
 
 #include "test.h"
+#include "cpu_relax.h"
 
 /*
  * Create NUMTHREADS threads in addition to the Main thread.
@@ -88,7 +89,7 @@ mythread(void * arg)
 	{
 	  int i;
 	  for (i = 0; i < 1E7; i++)
-	    __asm__ volatile ("pause":::);
+	    CPU_RELAX();
 	}
     }
 

winsup/testsuite/winsup.api/pthread/cancel5.c

@@ -38,12 +38,13 @@
  *
  * Fail Criteria:
  * - Process returns non-zero exit status.
- */
-
-#include "test.h"
-
-/*
- * Create NUMTHREADS threads in addition to the Main thread.
+ */
+
+#include "test.h"
+#include "cpu_relax.h"
+
+/*
+ * Create NUMTHREADS threads in addition to the Main thread.
  */
 enum {
   NUMTHREADS = 10
@@ -89,7 +90,7 @@ mythread(void * arg)
 	{
 	  int i;
 	  for (i = 0; i < 1E7; i++)
-	    __asm__ volatile ("pause":::);
+	    CPU_RELAX();
 	}
     }
 

winsup/testsuite/winsup.api/pthread/cpu_relax.h

@@ -0,0 +1,12 @@
+#ifndef CPU_RELAX_H
+#define CPU_RELAX_H
+
+#if defined(__x86_64__) || defined(__i386__)  // Check for x86 architectures
+   #define CPU_RELAX() __asm__ volatile ("pause" :::)
+#elif defined(__aarch64__) || defined(__arm__)  // Check for ARM architectures
+   #define CPU_RELAX() __asm__ volatile ("yield" :::)
+#else
+   #error unimplemented for this target
+#endif
+
+#endif