`cc` 1.0.86 seems to erroneously enable parallelism by default on certain platforms

[IGI-111]

Compiling openssl-sys on aarch64-unknown-linux-gnu, which uses cc fails with the following error:

 --- stderr
  make: *** read jobs pipe: Resource temporarily unavailable.  Stop.
  make: *** Waiting for unfinished jobs....
  thread 'main' panicked at /cargo/registry/src/index.crates.io-6f17d22bba15001f/openssl-src-300.2.3+3.2.1/src/lib.rs:611:9:



  Error building OpenSSL:
      Command: cd "/target/aarch64-unknown-linux-gnu/release/build/openssl-sys-6a5ed052a12e98be/out/openssl-build/build/src" && MAKEFLAGS="-j --jobserver-fds=7,8 --jobserver-auth=7,8" "make" "build_libs"
      Exit status: exit status: 2

This is a known issue with building openssl on this platform using parallelism:
rust-lang/cargo#13476
rust-openssl/rust-openssl#2179

However, the parallel feature is not enabled by openssl-sys and compiling with the exact same version of openssl-sys but using cc 1.0.83 succeeds, which leads me to believe there is a breaking change or bug in the 1.0.86 version.

[NobodyXu]

Duplicate of #962 , there's probably another crate that enables feature cc/parallel

To solve this problem once and for all, I believe we need to change rust-lang/jobserver.

A temporary fix can be done here for openssl-sys, by disabling O_NONBLOCK when the jobserver is not used, though it is racy and if you spawn make on another thread it could still fail, but it will work for openssl if its build.rs is single-thread only.

[IGI-111]

Indeed after some investigation I think I found another crate that enables it in my own build, since building openssl-sys on its own does not fail.

In this case it was libgit2-sys, which does so even when configured to vendor openssl.

Since this doesn't seem to be a cc issue, I'll close this.

Good luck trying to fix this permanently and thanks for the pointers.