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/build_libpng.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+set -euo pipefail
+
+pngver=1.6.43
+
+## Grab sources and check them
+
+curl -LOJ "http://prdownloads.sourceforge.net/libpng/libpng-$pngver.tar.xz?download"
+# Brew doesn't provide any sha256sum, so we're making do with `sha2` instead.
+if [ "$(sha2 -q -256 libpng-$pngver.tar.xz)" != 6a5ca0652392a2d7c9db2ae5b40210843c0bbc081cbd410825ab00cc59f14a6c ]; then
+	sha2 -256 libpng-$pngver.tar.xz
+	echo Checksum mismatch! Aborting. >&2
+	exit 1
+fi
+
+## Extract sources and patch them
+
+tar -xvf libpng-$pngver.tar.xz
+
+## Start building!
+
+mkdir -p build
+cd build
+../libpng-$pngver/configure --disable-shared --enable-static \
+	CFLAGS="-O3 -flto -DNDEBUG -mmacosx-version-min=10.9 -arch x86_64 -arch arm64 -fno-exceptions"
+make -kj
+make install prefix="$PWD/../libpng-staging"

.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+		# instead of the outdated one preinstalled on macOS (which doesn't even support `-Wall`...)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'"

.github/scripts/mingw-w64-libpng-dev.sh

@@ -1,5 +1,5 @@
-#!/bin/sh
-set -e
+#!/bin/bash
+set -euo pipefail
 
 pngver=1.6.43
 arch="$1"
@@ -27,7 +27,7 @@ cd build
 	--prefix="/usr/$arch" \
 	--enable-shared --disable-static \
 	CPPFLAGS="-D_FORTIFY_SOURCE=2" \
-	CFLAGS="-O2 -pipe -fno-plt -fexceptions --param=ssp-buffer-size=4" \
+	CFLAGS="-O2 -pipe -fno-plt -fno-exceptions --param=ssp-buffer-size=4" \
 	LDFLAGS="-Wl,-O1,--sort-common,--as-needed -fstack-protector"
 make -kj
-make install
+sudo make install