Build “fat binaries” for macOS (#1461)

The same binary, both for Intel and ARM Macs!

Builds libpng manually since the lib Brew distributes only contains code for the host arch.

.github/scripts/install_deps.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -e
+set -euo pipefail
 
 case "${1%-*}" in
 	ubuntu)
@@ -7,9 +7,11 @@ case "${1%-*}" in
 		sudo apt-get install -yq bison libpng-dev pkg-config
 		;;
 	macos)
-		brew install bison libpng pkg-config md5sha1sum
-		# For the version check below exclusively, re-do this before building
-		export PATH="/opt/homebrew/opt/bison/bin:/usr/local/opt/bison/bin:$PATH"
+		brew install bison sha2 md5sha1sum
+		# Export `bison` to allow using the version we install from Homebrew,
+		# instead of the outdated one preinstalled on macOS (which doesn't even support `-Wall`...)
+		export PATH="/opt/homebrew/opt/bison/bin:$PATH"
+		printf 'PATH=%s\n' "$PATH" >>"$GITHUB_ENV" # Make it available to later CI steps too
 		;;
 	*)
 		echo "WARNING: Cannot install deps for OS '$1'"