Add HOMEBREW_ARCH environment variable

[dalance]

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I want to use HOMEBREW_ARCH environment variable proposed at #4831.
This is because my home directory is shared by NFS through hosts with variety architectures.
Now I do brew install at an oldest host carefully, but this is inconvenience.

[MikeMcQuaid]

Please provide more details of your use-case, OS, etc. for discussion.

[dalance]

In my environment, I use the following hosts and share home directory by NFS.

• OS
  • CentOS7.6
• CPU
  • host1: Intel(R) Xeon(R) Gold 6134
  • host2: Intel(R) Xeon(R) Silver 4108
  • host3: Intel(R) Xeon(R) CPU E5-2620 v4
  • host4: Intel(R) Xeon(R) CPU E5-2695 v3
  • host5: Intel(R) Xeon(R) CPU L5630
  • host6: AMD Ryzen Threadripper 1950X

For example, if I do brew install python3 at host1,
python3 command will abort at host3, host4, host5, host6 like below:

[1]    106302 illegal hardware instruction (core dumped)  python3

git, tmux, neovim become the same result.

If I do brew install at host5 (this is the oldest arch), all binaries work fine at all hosts.
Alternatively If I set HOMEBREW_ARCH=nehalem with this PR, work fine too.

[MikeMcQuaid]

OS

• CentOS7.6

Gotcha. As this should be made on Linux-only please make this change in Library/Homebrew/extend/os/linux/hardware.rb using a similar pattern to Library/Homebrew/extend/os/mac/hardware.rb and Library/Homebrew/hardware.rb.

[dalance]

I tried to move the change to Library/Homebrew/extend/os/linux/hardware/cpu.rb.

[MikeMcQuaid]

Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @dalance!

[dalance]

Thanks!