Check for features support

Hello,

Is there an easy way to check whether a CPU supports FEAT_DotProd and/or FEAT_I8MM ?

I can successfully build the project but trying to run kleidiai_test fails with:

❯ file kleidiai_test                                                                                                                                                                                  (kleidiai-env) 
kleidiai_test: ELF 64-bit LSB pie executable, ARM aarch64, version 1 (GNU/Linux), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 3.7.0, with debug_info, not stripped

❯ ./kleidiai_test                                                                                                                                                                                     (kleidiai-env) 
Running main() from /home/mgrigorov/git/kleidiai/build/_deps/googletest-src/googletest/src/gtest_main.cc
[==========] Running 151 tests from 5 test suites.
[----------] Global test environment set-up.
[----------] 1 test from matmul_clamp_f32_qsi8d32p4x8_qsi4c32p4x8_8x4x32_neon_i8mm
[ RUN      ] matmul_clamp_f32_qsi8d32p4x8_qsi4c32p4x8_8x4x32_neon_i8mm.EndToEnd
fish: Job 1, './kleidiai_test' terminated by signal SIGILL (Illegal instruction)

The CPU is Hisilicon Kunpeng 920:

❯ lscpu                                                                                                                                                                                               (kleidiai-env) 
Architecture:           aarch64
  CPU op-mode(s):       64-bit
  Byte Order:           Little Endian
CPU(s):                 8
  On-line CPU(s) list:  0-7
Vendor ID:              HiSilicon
  Model name:           Kunpeng-920
    Model:              0
    Thread(s) per core: 1
    Core(s) per socket: 8
    Socket(s):          1
    Stepping:           0x1
    Frequency boost:    disabled
    CPU max MHz:        2400.0000
    CPU min MHz:        2400.0000
    BogoMIPS:           200.00
    Flags:              fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm jscvt fcma dcpop asimddp asimdfhm
Caches (sum of all):    
  L1d:                  512 KiB (8 instances)
  L1i:                  512 KiB (8 instances)
  L2:                   4 MiB (8 instances)
  L3:                   32 MiB (1 instance)
NUMA:                   
  NUMA node(s):         1
  NUMA node0 CPU(s):    0-7
Vulnerabilities:        
  Gather data sampling: Not affected
  Itlb multihit:        Not affected
  L1tf:                 Not affected
  Mds:                  Not affected
  Meltdown:             Not affected
  Mmio stale data:      Not affected
  Retbleed:             Not affected
  Spec rstack overflow: Not affected
  Spec store bypass:    Vulnerable
  Spectre v1:           Mitigation; __user pointer sanitization
  Spectre v2:           Not affected
  Srbds:                Not affected
  Tsx async abort:      Not affected

AFAIK this CPU implements ARMv8.2a and according to "Current supported Arm® CPUs technologies and features" those features are optional in 8.2, so I am not sure whether the "Illegal instruction" failure is caused by a missing feature.

Would it be a good idea to add a Cmake check for the features/instructions and fail early at build time (cmake ...) if a feature is not supported on the build machine ? Similar for runtime: add a check and give better error message to the user instead of failing with SIGILL.

Thank you!