Support s390/s390x in performance schema's cycle-counting functions.
Filed upstream at http://bugs.mysql.com/bug.php?id=59953

diff -up mysql-8.0.17/include/my_rdtsc.h.patch2 mysql-8.0.17/include/my_rdtsc.h
--- mysql-8.0.17/include/my_rdtsc.h.patch2	2019-06-25 12:23:30.000000000 +0200
+++ mysql-8.0.17/include/my_rdtsc.h	2019-07-22 19:02:43.824388869 +0200
@@ -128,5 +128,6 @@ void my_timer_init(MY_TIMER_INFO *mti);
 #define MY_TIMER_ROUTINE_GETSYSTEMTIMEASFILETIME 26
 #define MY_TIMER_ROUTINE_ASM_SUNPRO_X86_64 27
 #define MY_TIMER_ROUTINE_ASM_AARCH64 28
+#define MY_TIMER_ROUTINE_ASM_S390 29
 
 #endif
diff -up mysql-8.0.17/mysys/my_rdtsc.cc.patch2 mysql-8.0.17/mysys/my_rdtsc.cc
--- mysql-8.0.17/mysys/my_rdtsc.cc.patch2	2019-06-25 12:23:30.000000000 +0200
+++ mysql-8.0.17/mysys/my_rdtsc.cc	2019-07-22 19:04:03.227227901 +0200
@@ -204,6 +204,13 @@ ulonglong my_timer_cycles(void) {
     __asm __volatile__("mrs %[rt],cntvct_el0" : [ rt ] "=r"(result));
     return result;
   }
+#elif defined(__GNUC__) && defined(__s390__)
+  /* covers both s390 and s390x */
+  {
+    ulonglong result;
+    __asm__ __volatile__ ("stck %0" : "=Q" (result) : : "cc");
+   return result;
+  }
 #elif defined(HAVE_SYS_TIMES_H) && defined(HAVE_GETHRTIME)
   /* gethrtime may appear as either cycle or nanosecond counter */
   return (ulonglong)gethrtime();
@@ -505,6 +512,8 @@ void my_timer_init(MY_TIMER_INFO *mti) {
   mti->cycles.routine = MY_TIMER_ROUTINE_ASM_GCC_SPARC32;
 #elif defined(__GNUC__) && defined(__aarch64__)
   mti->cycles.routine = MY_TIMER_ROUTINE_ASM_AARCH64;
+#elif defined(__GNUC__) && defined(__s390__)
+  mti->cycles.routine = MY_TIMER_ROUTINE_ASM_S390;
 #elif defined(HAVE_SYS_TIMES_H) && defined(HAVE_GETHRTIME)
   mti->cycles.routine = MY_TIMER_ROUTINE_GETHRTIME;
 #else