Do not assume that std::int64_t is long int

[laurynas-biveinis]

Use PRId64 macro to printf-format an int64_t value.

This fixes

storage/perfschema/unittest/pfs-t.cc:2667:8: error: format specifies type 'long' but the argument has type 'int64_t' (aka 'long long') [-Werror,-Wformat]
2666 | ok(cpu_stat.m_delay_start == delay_start, "delay start %ld",
| ~~~
| %lld
2667 | cpu_stat.m_delay_start);
| ^~~~~~~~~~~~~~~~~~~~~~
storage/perfschema/unittest/pfs-t.cc:2669:8: error: format specifies type 'long' but the argument has type 'int64_t' (aka 'long long') [-Werror,-Wformat]
2668 | ok(cpu_stat.m_delay_total_ns == delay_total, "delay total %ld",
| ~~~
| %lld
2669 | cpu_stat.m_delay_total_ns);
| ^~~~~~~~~~~~~~~~~~~~~~~~~
storage/perfschema/unittest/pfs-t.cc:2671:8: error: format specifies type 'long' but the argument has type 'int64_t' (aka 'long long') [-Werror,-Wformat]
2670 | ok(cpu_stat.m_cpu_start == quantum_start, "cpu start %ld",
| ~~~
| %lld
2671 | cpu_stat.m_cpu_start);
| ^~~~~~~~~~~~~~~~~~~~
storage/perfschema/unittest/pfs-t.cc:2673:8: error: format specifies type 'long' but the argument has type 'int64_t' (aka 'long long') [-Werror,-Wformat]
2672 | ok(cpu_stat.m_cpu_total_ns == cpu_total, "cpu total %ld",
| ~~~
| %lld
2673 | cpu_stat.m_cpu_total_ns);
| ^~~~~~~~~~~~~~~~~~~~~~~

Squash with b4f911b