brew.sh: set HOMEBREW_FORCE_HOMEBREW_ON_LINUX when core repo is homeb…

…rew-core

See Homebrew/install#571

When the install script sets as https://github.com/Homebrew/homebrew-core,
we need to use the homebrew-core bottle domain, and correctly set
the HOMEBREW_CORE_DEFAULT_GIT_REMOTE below.

This also fixes the brew doctor issue for new homebrew-core Linux installations

Warning: Suspicious https://github.com/Homebrew/linuxbrew-core git origin remote found.
The current git origin is:
  https://github.com/Homebrew/homebrew-core

With a non-standard origin, Homebrew won't update properly.
You can solve this by setting the origin remote:
  git -C "/home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-core" remote set-url origin https://github.com/Homebrew/linuxbrew-core

Library/Homebrew/brew.sh

@@ -353,6 +353,16 @@ then
   export HOMEBREW_FORCE_HOMEBREW_ON_LINUX="1"
 fi
 
+HOMEBREW_CORE_REPOSITORY_ORIGIN="$(git -C "${HOMEBREW_CORE_REPOSITORY}" remote get-url origin)"
+
+if [[ -n "${HOMEBREW_LINUX}" && "${HOMEBREW_CORE_REPOSITORY_ORIGIN}" = "https://github.com/Homebrew/homebrew-core" ]]
+then
+  # If the remote origin has been set to Homebrew/homebrew-core by the install script,
+  # then we are in the case of a new installation of brew, using Homebrew/homebrew-core as a Linux core repository.
+  # In that case, set HOMEBREW_FORCE_HOMEBREW_ON_LINUX=1 to set the right HOMEBREW_BOTTLE_DOMAIN below.
+  export HOMEBREW_FORCE_HOMEBREW_ON_LINUX="1"
+fi
+
 if [[ -n "${HOMEBREW_MACOS}" ]]
 then
   HOMEBREW_PRODUCT="Homebrew"