bottle merge: add support for linux cellar

[iMichka]

The first attempt to build and pull a formula (hello) for linux in homebrew-core
resulted in a wrong cellar line being added to the formula's bottle block.

How to test/debug this, using the 4 bottles that where built for hello:
brew bottle --merge --debug hello--2.10_1.mojave.bottle.json hello--2.10_1.x86_64_linux.bottle.json hello--2.10_1.big_sur.bottle.json hello--2.10_1.catalina.bottle.json

This command would add create the following bottle block:

bottle do
cellar "/home/linuxbrew/.linuxbrew/Cellar"
sha256 "a0af7dcbb5c83f6f3f7ecd507c2d352c1a018f894d51ad241ce8492fa598010f" => :big_sur
sha256 "5334dd344986e46b2aa4f0471cac7b0914bd7de7cb890a34415771788d03f2ac" => :catalina
sha256 "22948764d8f8d7be4870ff92dae64d986eb63a9150b219c20fff87d1a6aa93d6" => :mojave
sha256 "702dc7f78444d2f4f1c19324be654bcbb8b99dd0e9ce26c3e2fbc3b6464a189f" => :x86_64_linux
end

After the change in this PR, the result is the following:

bottle do
sha256 "a0af7dcbb5c83f6f3f7ecd507c2d352c1a018f894d51ad241ce8492fa598010f" => :big_sur
sha256 "5334dd344986e46b2aa4f0471cac7b0914bd7de7cb890a34415771788d03f2ac" => :catalina
sha256 "22948764d8f8d7be4870ff92dae64d986eb63a9150b219c20fff87d1a6aa93d6" => :mojave
sha256 "702dc7f78444d2f4f1c19324be654bcbb8b99dd0e9ce26c3e2fbc3b6464a189f" => :x86_64_linux
end

The brew bottle --merge code will pick the most common cellar line between the 4 bottles, by order of priority:

• non-relocatable (fixed cellar path)
• cellar :any
• cellar :any_skip_relocation

In the case of the hello bottle, the 3 mac bottles are "cellar :any_skip_relocation", and the linux bottle
is non-relocatable. So the linux bottle wins and the code correctly determines that the 4 bottles should
be non-relocatable.

In that case, the /home/linuxbrew/.linuxbrew/Cellar path is defined as cellar, and by convention
we do not write that out to the formula file, hence the cellar path check that needs to be modified
in this PR.

This PR also fixes the same situation for mac ARM cellar paths

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• Have you added an explanation of what your changes do and why you'd like us to include them?
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• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?
• Have you successfully run brew man locally and committed any changes?

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[BrewTestBot]

Review period will end on 2020-11-27 at 13:41:08 UTC.

[iMichka]

Thanks @MikeMcQuaid , I made the asked changes. I was wondering why there was a hard-coded "/usr/local/Cellar" in there but it was probably a legacy piece of code that never got updated :)

[iMichka]

Follow-up issue: #9315

[BrewTestBot]

Review period ended.