[OpenMP] get logical core count on modern apple platform (llvm#87231)

`hw.logicalcpu` returns the available logical core count

Fix build error for watchOS

```
runtime/src/z_Linux_util.cpp:1821:8: error: 'host_info' is unavailable: not available on watchOS
  rc = host_info(mach_host_self(), HOST_BASIC_INFO, (host_info_t)&info, &num);
       ^
/Applications/Xcode_15.2.app/Contents/Developer/Platforms/WatchOS.platform/Developer/SDKs/WatchOS10.2.sdk/usr/include/mach/mach_host.h:82:15: note: 'host_info' has been explicitly marked unavailable here
kern_return_t host_info
              ^
1 warning and 1 error generated.
make[2]: *** [runtime/src/CMakeFiles/omp.dir/z_Linux_util.cpp.o] Error 1
```

Author: nihui

openmp/runtime/src/z_Linux_util.cpp

@@ -1889,21 +1889,8 @@ static int __kmp_get_xproc(void) {
 
 #elif KMP_OS_DARWIN
 
-  // Bug C77011 High "OpenMP Threads and number of active cores".
-
-  // Find the number of available CPUs.
-  kern_return_t rc;
-  host_basic_info_data_t info;
-  mach_msg_type_number_t num = HOST_BASIC_INFO_COUNT;
-  rc = host_info(mach_host_self(), HOST_BASIC_INFO, (host_info_t)&info, &num);
-  if (rc == 0 && num == HOST_BASIC_INFO_COUNT) {
-    // Cannot use KA_TRACE() here because this code works before trace support
-    // is initialized.
-    r = info.avail_cpus;
-  } else {
-    KMP_WARNING(CantGetNumAvailCPU);
-    KMP_INFORM(AssumedNumCPU);
-  }
+  size_t len = sizeof(r);
+  sysctlbyname("hw.logicalcpu", &r, &len, NULL, 0);
 
 #else