runtime: add freebsd free_memory() support

[kbkpbot]

Fix issue #23581

[huly-for-github]

Connected to Huly®: V_0.6-22020

[medvednikov]

FAIL  [45/69] C:   491.4 ms, R:     2.697 ms vlib/runtime/runtime_test.v
total memory: 8552550400
free  memory: 0
/tmp/cirrus-ci-build/vlib/runtime/runtime_test.v:8: fn test_physical_memory
  > assert total > 0 && free > 0
    Left value (len: 4): `true`
   Right value (len: 5): `false`

    nr cpus: 2
    nr jobs: 1
   is_32bit: false
   is_64bit: true
      is_le: true
      is_be: false

[spytheman]

Excellent work.