Auto merge of #10427 - weihanglo:drop-num_cpus, r=joshtriplett

Use `available_parallelism` instead of `num_cpus`

diff --cc Cargo.toml
index f05ddd9249b6570a5e072f7e8f5defffa09e3edc,baa20a8c7b89883684e9e70e4ba689c1f7ca9aa4..148db4262b046661141dc56e30d1c03b56d8d6a3
--- 1/Cargo.toml
--- 2/Cargo.toml
+++ b/Cargo.toml
@@@ -41,9 -41,8 +41,8 @@@ jobserver = "0.1.24
  lazycell = "1.2.0"
  libc = "0.2"
  log = "0.4.6"
 -libgit2-sys = "0.12.24"
 +libgit2-sys = "0.13.1"
  memchr = "2.1.3"
- num_cpus = "1.0"
  opener = "0.5"
  os_info = "3.0.7"
  percent-encoding = "2.0"