CI: Run Linux AArch64 tests on real hardware using Cirrus CI

[tatsuya6502]

This PR adds Cirrus CI job to run Linux AArch64 tests on real hardware.

[tatsuya6502]

It seems we need to install pkg-config and openssl library on Cirrus CI containers.
https://cirrus-ci.com/task/5134163287212032

Trying to run the docker images locally to figure out what will be needed.

[tatsuya6502]

It is interesting.

• All tests are passing on the rustlang's Rust nightly image.
• The following tests are failing on the Docker's official Rust images (stable and MSRV).

failures:
    sync::cache::tests::drop_value_immediately_after_eviction
    sync::cache::tests::get_with
    sync::cache::tests::get_with_if
    sync::cache::tests::test_key_lock_used_by_immediate_removal_notifications
    sync::cache::tests::try_get_with
    sync::segment::tests::drop_value_immediately_after_eviction
    sync::segment::tests::get_with_if
    sync::segment::tests::try_get_with

https://cirrus-ci.com/build/6464088501911552

[tatsuya6502]

The following tests are failing on the Docker's official Rust images (stable and MSRV).

Fixed them by limiting the numbers of concurrent jobs and test threads for cargo test.

env:
  NUM_CPUS: "2"

linux_arm64_task:
  arm_container:
    cpu: $NUM_CPUS
    matrix:
      - image: rust:slim  # docker's official latest rust stable version
      - image: rustlang/rust:nightly-slim # nightly hosted by rustlang
      - image: rust:1.51.0-slim # MSRV

  test_script:
    # Run tests (debug, sync feature)
    - cargo test -j 1 --lib --features sync -- --test-threads=$NUM_CPUS
    - ...

I found that Cirrus CI environment exposes the real number of CPU cores (64 cores) of the node, while it is allowing the test container to use only 2 cores. This made cargo test to run a way more tests at the same time, and unit tests in Moka tend to spawn many threads, causing some threads not to be given enough CPU time.

$ nproc
64

$ lscpu
Architecture:                    aarch64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
CPU(s):                          64
On-line CPU(s) list:             0-63
Thread(s) per core:              1
Core(s) per socket:              64
Socket(s):                       1
NUMA node(s):                    1
Vendor ID:                       ARM
Model:                           1
Model name:                      Neoverse-N1
Stepping:                        r3p1
BogoMIPS:                        243.75
L1d cache:                       4 MiB
L1i cache:                       4 MiB
L2 cache:                        64 MiB
L3 cache:                        32 MiB
NUMA node0 CPU(s):               0-63
Vulnerability Itlb multihit:     Not affected
Vulnerability L1tf:              Not affected
Vulnerability Mds:               Not affected
Vulnerability Meltdown:          Not affected
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:        Mitigation; __user pointer sanitization
Vulnerability Spectre v2:        Not affected
Vulnerability Srbds:             Not affected
Vulnerability Tsx async abort:   Not affected
Flags:                           fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs

[tatsuya6502]

Merging.