zsh_completion: fix brew config.

Signed-off-by: Xu Cheng <xucheng@me.com>

Closes #28878.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
ghc: bump revision for new core GCC formula.

Closes #28654.
ghc: update 7.6.3 bottle.

Closes #28849.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>