Merge #1072: ci: Attempt to make macOS builds more reliable

d9396a5 ci: Attempt to make macOS builds more reliable (Tim Ruffing)

Pull request description:

ACKs for top commit:
  jonasnick:
    ACK d9396a5

Tree-SHA512: 68df44107d74671de148e9c3e6dbc6b16bec937137d7d9771efce10f5d66459559b372346d05ecc23237b2e3af9479156f733219717cb93f5204f9ea5b2636a9

.cirrus.yml

@@ -135,7 +135,9 @@ task:
  ## - rm /tmp/.com.apple.dt.CommandLineTools.installondemand.in-progress
  ##
  brew_valgrind_pre_script:
- - brew update
+ # Reinstall brew. We could do `brew update` instead but that often fails.
+ - /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/uninstall.sh)"
+ - /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
  - brew config
  - brew tap LouisBrunner/valgrind
  # Fetch valgrind source but don't build it yet.