[rocm-libraries] ROCm/rocm-libraries#9667 (commit 8b95262)

fix: [CK] Fix the multiple targets build OOM failure

JIRA ID : AICK-1716

## Motivation

Fix the multiple targets build OOM failure caused by hardcoded ninja
-j64 parallelism on a weaker agent (i.e. 25 cores) in CK CI builds 1793
and 1830.

## Technical Details

Use nthreads() to query the actual agent core count at runtime and caps
at 64, so it will never over-subscribe the machine.

## Test Plan

Run the multiple targets build and make sure the core count as expected
without over-subscribing the machine. And pass the test.

## Test Result

Passed.

## Submission Checklist

- [x] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.