[base] Fix the return of ClockNow on IBMi

The API thread_cputime() is only defined but not yet implemented on IBMi.

Change-Id: I8ea7ff724e749f537b54e75a00d718500807ca8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1957831
Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#65392}

src/base/platform/time.cc

@@ -70,6 +70,9 @@ V8_INLINE int64_t ClockNow(clockid_t clk_id) {
 #if defined(V8_OS_AIX)
   thread_cputime_t tc;
   if (clk_id == CLOCK_THREAD_CPUTIME_ID) {
+#if defined(__PASE__)  // CLOCK_THREAD_CPUTIME_ID clock not supported on IBMi
+    return 0;
+#endif
     if (thread_cputime(-1, &tc) != 0) {
       UNREACHABLE();
     }